Map of The Universe

Astronomers Make The Largest Map of The Universe Yet[1]

The image at left shows a slice through largest-ever three-dimensional map of the Universe. Earth is at the left, and distances to galaxies and quasars are labelled by the lookback time to the objects (lookback time means how long the light from an object has been traveling to reach us here on Earth).

The locations of quasars (galaxies with supermassive black holes) are shown by the red dots, and nearer galaxies mapped by SDSS are also shown (yellow). The right-hand edge of the map is the limit of the observable Universe, from which we see the Cosmic Microwave Background (CMB)–the light “left over” from the Big Bang. The bulk of the empty space in between the quasars and the edge of the observable universe are from the “dark ages”, prior to the formation of most stars, galaxies, or quasars. [Credit: Anand Raichoor (École polytechnique fédérale de Lausanne, Switzerland) and the SDSS collaboration.]

Astronomers with the Sloan Digital Sky Survey (SDSS) have created the first map of the large-scale structure of the Universe based entirely on the positions of quasars. Quasars are the incredibly bright and distant points of light powered by supermassive black holes.

“Because quasars are so bright, we can see them all the way across the Universe,” said Ashley Ross of the Ohio State University, the co-leader of the study. “That makes them the ideal objects to use to make the biggest map yet.”

The amazing brightness of quasars is due to the supermassive black holes found at their centers. As matter and energy fall into a quasar’s black hole, they heat up to incredible temperatures and begin to glow. It is this bright glow that is detected by a dedicated 2.5-meter telescope here on Earth.

“These quasars are so far away that their light left them when the Universe was between three and seven billion years old, long before the Earth even existed,” said Gongbo Zhao from the National Astronomical Observatories of Chinese Academy of Sciences, the study’s other co-leader.

To make their map, scientists used the Sloan Foundation Telescope to observe an unprecedented number of quasars. During the first two years of the SDSS’s Extended Baryon Oscillation Spectroscopic Survey (eBOSS), astronomers measured accurate three-dimensional positions for more than 147,000 quasars.

The telescope’s observations gave the team the quasars’ distances, which they used to create a three-dimensional map of where the quasars are. But to use the map to understand the expansion history of the Universe, they had to go a step further, using a clever technique involving studying “baryon acoustic oscillations” (BAOs). BAOs are the present-day imprint of sound waves which travelled through the early Universe, when it was much hotter and denser than the universe we see today. But when the universe was 380,000 years old, conditions changed suddenly and the sound waves became “frozen” in place. These frozen waves are left imprinted in the three-dimensional structure of the Universe we see today.

The good news about these frozen waves—the original baryon acoustic oscillations—is that the process that produced them is simple. Thus, we have a good understanding of what BAOs must have looked like at that ancient time. When we look at the three-dimensional structure of the Universe today, it contains these same BAOs grown out to a huge scale by the expansion of the Universe. The observed size of the BAO can be used as a “standard ruler” to measure distances. Just as by using the apparent angle of a meter stick viewed from the other side of a football field, you can estimate the length of the field. “You have meters for small units of length, kilometers or miles for distances between cities, and we have the BAO scale for distances between galaxies and quasars in cosmology,” explained Pauline Zarrouk, a PhD student at the Irfu/CEA, University Paris-Saclay, who measured the projected BAO scale.

Astronomers from the SDSS have previously used the BAO technique on nearby galaxies and then on intergalactic gas distributions to push this analysis farther and farther back in time. The current results cover a range of times where they have never been observed before, measuring the conditions when the universe more than two billion years before the Earth formed.

The results of the new study confirm the standard model of cosmology that researchers have built over the last twenty years. In this standard model, the Universe follows the predictions of Einstein’s general theory of relativity—but includes components whose effects we can measure, but whose causes we do not understand. Along with the ordinary matter that makes up stars and galaxies, the universe includes dark matter—invisible yet still affected by gravity—and a mysterious component called “dark energy.” Dark energy is the dominant component at the present time, and it has special properties that cause the expansion of the universe to speed up.

“Our results are consistent with Einstein’s theory of general relativity,” said Hector Gil-Marin, a researcher from the Laboratoire de Physique Nucléaire et de hautes Énergies in Paris who undertook key parts of the analysis. “We now have BAO measurements covering a range of cosmological distances, and they all point to the same thing: the simple model matches the observations very well.”

Even though we understand how gravity works, we still do not understand everything—there is still the question of what exactly dark energy is. “We would like to understand dark energy further,” said Will Percival from the University of Portsmouth, who is the eBOSS survey scientist. “Surveys like eBOSS are helping us to build up our understanding of how dark energy fits into the story of the universe.”

The eBOSS experiment is still continuing, using the Sloan Telescope at Apache Point Observatory in New Mexico, USA. As astronomers with eBOSS observe more quasars and nearby galaxies, the size of their map will continue to increase. After eBOSS is complete, a new generation of sky surveys will begin, including the Dark Energy Spectroscopic Instrument (DESI) and the European Space Agency Euclid satellite mission. These will increase the fidelity of the maps by a factor of ten compared with eBOSS, revealing the universe and dark energy in unprecedented detail.

[1] “Astronomers Make The Largest Map of The Universe Yet,” Astronomy Now (22 May 2017)

Dying Stars Give Newborn Black Holes A Swift Kick

Dying Stars Give Newborn Black Holes A Swift Kick[1]

For nearly 30 years I [Fred L. Wilson] taught at RIT. The astrophysics program at RIT is new since I taught there. The program is exemplary in research and instruction in astronomy, physics, and astrophysics. I remain a Professor Emeritus from RIT

New information gleaned from gravitational wave observations is helping scientists understand what happens when massive stars die and transform into black holes.

Rochester Institute of Technology researcher Richard O’Shaughnessy and collaborators reanalyzed the merging black holes detected by LIGO (Laser Interferometer Gravitational Wave Observatory) on Dec. 26, 2016.

“Using essentially freshman physics, we drew new insights about the most violent events in the universe,” said O’Shaughnessy, an associate professor in RIT’s School of Mathematical Sciences. He is also researcher in RIT’s Center for Computational Relativity and Gravitation and a member of the LIGO Scientific Collaboration.

O’Shaughnessy presented his research findings at the American Astronomical Society meeting on June 5 in Austin, Texas. Physical Review Letters has accepted a paper co-authored by O’Shaughnessy, Davide Gerosa from Caltech and Daniel Wysocki from RIT.

The LIGO Scientific Collaboration cited O’Shaughnessy’s research in the paper announcing its third discovery of gravitational waves that published in Physical Review Letters on June 1.

The current study reanalyzed the binary black holes, known as GW151226. It has been the only time LIGO has reported binary black holes must be spinning, O’Shaughnessy said. LIGO’s previous measurements suggested that the larger mass orbited the other at a slightly tilted angle.

O’Shaughnessy and his team link the black hole’s misalignment to when it formed from the death of a massive star. The force of the stellar explosion and collapse expelled the newborn black hole with a “natal kick,” causing this misalignment, the authors suggest.

Natal kicks are thought to occur during the formation of neutron stars, which are created from the death of less massive stars than the progenitors of LIGO’s sources. O’Shaughnessy’s team suggests this phenomenon could also apply to binary black holes, which orbit each other.

“My collaborators and I tried to constrain the strength of these natal kicks based on LIGO’s observation,” O’Shaughnessy said. “If it formed from an isolated pair of stars, we conclude strong black hole natal kicks were required. That’s an exciting challenge for models of how massive stars explode and collapse.”

Gerosa adds, “Our study corroborates years of tentative but suggestive evidence that black holes might have received these kicks. And with just one of LIGO’s observations, we learned something about how a star exploded billions of years ago. That’s the promise of gravitational wave astronomy in action.”

This research has been supported by the National Science Foundation and NASA.

Davide Gerosa is supported by NASA through Einstein Postdoctoral Fellowship grant No. PF6-170152 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. Any opinions, findings, and conclusions or recommendations expressed in this article are those of the author and do not necessarily reflect the views of the Smithsonian Astrophysical Observatory or the National Aeronautics Space Administration.

[1]Susan Gawlowicz, “RIT study suggests Gravitational wave astronomy sheds light on supernova explosions,” Rochester Institute of Technology, University News (June 5, 2017)

New Map of the Universe

Astronomers Make The Largest Map of The Universe Yet[1]

The image at left shows a slice through largest-ever three-dimensional map of the Universe. Earth is at the left, and distances to galaxies and quasars are labelled by the lookback time to the objects (lookback time means how long the light from an object has been traveling to reach us here on Earth).

The locations of quasars (galaxies with supermassive black holes) are shown by the red dots, and nearer galaxies mapped by SDSS are also shown (yellow). The right-hand edge of the map is the limit of the observable Universe, from which we see the Cosmic Microwave Background (CMB)–the light “left over” from the Big Bang. The bulk of the empty space in between the quasars and the edge of the observable universe are from the “dark ages”, prior to the formation of most stars, galaxies, or quasars. [Credit: Anand Raichoor (École polytechnique fédérale de Lausanne, Switzerland) and the SDSS collaboration.]

Astronomers with the Sloan Digital Sky Survey (SDSS) have created the first map of the large-scale structure of the Universe based entirely on the positions of quasars. Quasars are the incredibly bright and distant points of light powered by supermassive black holes.

“Because quasars are so bright, we can see them all the way across the Universe,” said Ashley Ross of the Ohio State University, the co-leader of the study. “That makes them the ideal objects to use to make the biggest map yet.”

The amazing brightness of quasars is due to the supermassive black holes found at their centers. As matter and energy fall into a quasar’s black hole, they heat up to incredible temperatures and begin to glow. It is this bright glow that is detected by a dedicated 2.5-meter telescope here on Earth.

“These quasars are so far away that their light left them when the Universe was between three and seven billion years old, long before the Earth even existed,” said Gongbo Zhao from the National Astronomical Observatories of Chinese Academy of Sciences, the study’s other co-leader.

To make their map, scientists used the Sloan Foundation Telescope to observe an unprecedented number of quasars. During the first two years of the SDSS’s Extended Baryon Oscillation Spectroscopic Survey (eBOSS), astronomers measured accurate three-dimensional positions for more than 147,000 quasars.

The telescope’s observations gave the team the quasars’ distances, which they used to create a three-dimensional map of where the quasars are. But to use the map to understand the expansion history of the Universe, they had to go a step further, using a clever technique involving studying “baryon acoustic oscillations” (BAOs). BAOs are the present-day imprint of sound waves which travelled through the early Universe, when it was much hotter and denser than the universe we see today. But when the universe was 380,000 years old, conditions changed suddenly and the sound waves became “frozen” in place. These frozen waves are left imprinted in the three-dimensional structure of the Universe we see today.

The good news about these frozen waves—the original baryon acoustic oscillations—is that the process that produced them is simple. Thus, we have a good understanding of what BAOs must have looked like at that ancient time. When we look at the three-dimensional structure of the Universe today, it contains these same BAOs grown out to a huge scale by the expansion of the Universe. The observed size of the BAO can be used as a “standard ruler” to measure distances. Just as by using the apparent angle of a meter stick viewed from the other side of a football field, you can estimate the length of the field. “You have meters for small units of length, kilometers or miles for distances between cities, and we have the BAO scale for distances between galaxies and quasars in cosmology,” explained Pauline Zarrouk, a PhD student at the Irfu/CEA, University Paris-Saclay, who measured the projected BAO scale.

Astronomers from the SDSS have previously used the BAO technique on nearby galaxies and then on intergalactic gas distributions to push this analysis farther and farther back in time. The current results cover a range of times where they have never been observed before, measuring the conditions when the universe more than two billion years before the Earth formed.

The results of the new study confirm the standard model of cosmology that researchers have built over the last twenty years. In this standard model, the Universe follows the predictions of Einstein’s general theory of relativity—but includes components whose effects we can measure, but whose causes we do not understand. Along with the ordinary matter that makes up stars and galaxies, the universe includes dark matter—invisible yet still affected by gravity—and a mysterious component called “dark energy.” Dark energy is the dominant component at the present time, and it has special properties that cause the expansion of the universe to speed up.

“Our results are consistent with Einstein’s theory of general relativity,” said Hector Gil-Marin, a researcher from the Laboratoire de Physique Nucléaire et de hautes Énergies in Paris who undertook key parts of the analysis. “We now have BAO measurements covering a range of cosmological distances, and they all point to the same thing: the simple model matches the observations very well.”

Even though we understand how gravity works, we still do not understand everything—there is still the question of what exactly dark energy is. “We would like to understand dark energy further,” said Will Percival from the University of Portsmouth, who is the eBOSS survey scientist. “Surveys like eBOSS are helping us to build up our understanding of how dark energy fits into the story of the universe.”

The eBOSS experiment is still continuing, using the Sloan Telescope at Apache Point Observatory in New Mexico, USA. As astronomers with eBOSS observe more quasars and nearby galaxies, the size of their map will continue to increase. After eBOSS is complete, a new generation of sky surveys will begin, including the Dark Energy Spectroscopic Instrument (DESI) and the European Space Agency Euclid satellite mission. These will increase the fidelity of the maps by a factor of ten compared with eBOSS, revealing the universe and dark energy in unprecedented detail.

[1] “Astronomers Make The Largest Map of The Universe Yet,” Astronomy Now (22 May 2017)

No Universe without Big Bang

No Universe without Big Bang[1]

Researchers from the Max Planck Institute for Gravitational Physics in Potsdam and the Perimeter Institute in Canada disprove the theory of the “smooth beginning”

According to Einstein’s theory of relativity, the curvature of spacetime was infinite at the big bang. In fact, at this point all mathematical tools fail, and the theory breaks down. However, there remained the notion that perhaps the beginning of the universe could be treated in a simpler manner, and that the infinities of the big bang might be avoided. This has indeed been the hope expressed since the 1980s by the well-known cosmologists James Hartle and Stephen Hawking with their “no-boundary proposal”, and by Alexander Vilenkin with his “tunnelling proposal”. Now scientists at the Max Planck Institute for Gravitational Physics (Albert Einstein Institute/AEI) in Potsdam, Germany, and at the Perimeter Institute in Canada have been able to use better mathematical methods to show that these ideas cannot work. The big bang, in its complicated glory, retains all its mystery.

One of the principal goals of cosmology is to understand the beginning of our universe. Data from the Planck satellite mission shows that 13.8 billion years ago the universe consisted of a hot and dense soup of particles. Since then the universe has been expanding. This is the main tenet of the hot big bang theory, but the theory fails to describe the very first stages themselves, as the conditions were too extreme. Indeed, as we approach the big bang, the energy density and the curvature grow until we reach the point where they become infinite.

No smooth beginning

No “smooth beginning”: almost paradoxically, a smooth beginning causes large quantum fluctuations to grow (right), and thus prevents the development of a large universe as we know it (left). (J.-L. Lehners (Max Planck Institute for Gravitational Physics)

As an alternative, the “no-boundary” and “tunneling” proposals assume that the tiny early universe arose by quantum tunnelling from nothing, and subsequently grew into the large universe that we see. The curvature of spacetime would have been large, but finite in this beginning stage, and the geometry would have been smooth—without boundary (see Fig. 1, left panel). This initial configuration would replace the standard big bang. However, for a long time the true consequences of this hypothesis remained unclear. Now, with the help of better mathematical methods, Jean-Luc Lehners, group leader at the AEI, and his colleagues Job Feldbrugge and Neil Turok at Perimeter Institute, managed to define the 35-year-old theories in a precise manner for the first time, and to calculate their implications. The result of these investigations is that these alternatives to the big bang are no true alternatives. As a result of Heisenberg’s uncertainty relation, these models do not only imply that smooth universes can tunnel out of nothing, but also irregular universes. In fact, the more irregular and crumpled they are, the more likely (see Fig. 1, right panel). “Hence the “no-boundary proposal” does not imply a large universe like the one we live in, but rather tiny curved universes that would collapse immediately”, says Jean-Luc Lehners, who leads the “theoretical cosmology” group at the AEI.

Hence one cannot circumvent the big bang so easily. Lehners and his colleagues are now trying to figure out what mechanism could have kept those large quantum fluctuations in check under the most extreme circumstances, allowing our large universe to unfold.

[1] Max Planck Institute for Gravitational Physics, “No Universe without Big Bang,” (June 15, 2017).

Black Hole Merger

Third Gravitational Wave Detection, From Black-Hole Merger[1]

An artist’s conception shows two merging black holes similar to those detected by LIGO. Astronomers said Thursday (June 7, 2017) that they had felt space-time vibrations known as gravitational waves from the merger of a pair of mammoth black holes resulting in a pit of infinitely deep darkness. (Credit Aurore Simonnet/Sonoma State/Caltech/MIT/LIGO)

The void is rocking and rolling with invisible cataclysms.

Astronomers said Thursday (June 7, 2017) that they had felt space-time vibrations known as gravitational waves from the merger of a pair of mammoth black holes resulting in a pit of infinitely deep darkness weighing as much as 49 suns, some 3 billion light-years from here.

This is the third black-hole smashup that astronomers have detected since they started keeping watch on the cosmos back in September 2015, with LIGO, the Laser Interferometer Gravitational-Wave Observatory. All of them are more massive than the black holes that astronomers had previously identified as the remnants of dead stars.

In less than two short years, the observatory has wrought twin revolutions. It validated Einstein’s longstanding prediction that space-time can shake like a bowlful of jelly when massive objects swing their weight around, and it has put astronomers on intimate terms with the most extreme objects in his cosmic zoo and the ones so far doing the shaking: massive black holes.

“We are moving in a substantial way away from novelty towards where we can seriously say we are developing black-hole astronomy,” said David Shoemaker, a physicist at the Massachusetts Institute of Technology and spokesman for the LIGO Scientific Collaboration, an international network of about 1,000 astronomers and physicists who use the LIGO data. They and a similar European group named Virgo are collectively the 1,300 authors of a report on the most recent event that will be published in the journal Physical Review Letters on Thursday.

“We’re starting to fill in the mass spectrum of black holes in the universe,” said David Reitze, director of the LIGO Laboratory, a smaller group of scientists headquartered at Caltech and M.I.T. who built and run the observatory.

The National Science Foundation, which poured $1 billion into LIGO over 40 years, responded with pride. “This is exactly what we hoped for from N.S.F.’s investment in LIGO: taking us deeper into time and space in ways we couldn’t do before the detection of gravitational waves,” France Cordova, the foundation’s director, said in a statement. “In this case, we’re exploring approximately 3 billion light-years away!”

In the latest LIGO event, a black hole 19 times the mass of the Sun and another black hole 31 times the Sun’s mass, married to make a single hole of 49 solar masses. During the last frantic moments of the merger, they were shedding more energy in the form of gravitational waves than all the stars in the observable universe.

After a journey lasting 3 billion years, that is to say, a quarter of the age of the universe, those waves started jiggling LIGO’s mirrors back and forth by a fraction of an atomic diameter 20 times a second. The pitch rose to 180 cycles per second in about a tenth of a second before cutting off.

Zsuzsanna Marka, an astronomer at Columbia University, was sitting in an office on the morning of Jan. 4, 2017 when she got an email alert. She started to smile but then remembered she was not alone and the other person was not a member of LIGO, so she couldn’t say why she was smiling.

“I just kept smiling,” she said.

Upon further analysis it proved to be a perfect chirp, as predicted by Einstein’s equations. Because of the merger’s great distance, the LIGO scientists were able to verify that different frequencies of gravity waves all travel at the same speed, presumably the speed of light. As Dr. Reitze said, “Once again Einstein triumphs.”

“That’s not surprising,” Dr. Reitze went on, adding, “at some point he’s going to be wrong, and we’ll be looking.”

Poor Einstein.

Black holes were an entirely unwelcome consequence of his theory of general relativity that ascribes gravity to the warping of space-time geometry by matter and energy. Too much mass in one place, the equations said, could cause space to wrap itself around in a ball too tight and dense for even light to escape. In effect, Einstein’s theory suggested, matter, say a dead star, could disappear from the universe, leaving behind nothing but its gravitational ghost.

Einstein thought that nature would have more sense than that. But astronomers now agree that the sky is dotted with the dense dark remnants of stars that have burned up all their fuel and collapsed, often in gigantic supernova explosions. Until now, they were detectable only indirectly by the glow of x rays or other radiation from doomed matter heated to stupendous degrees as it swirls around a cosmic drain.

But what telescopes cannot see, gadgets like LIGO now can feel, or “hear.”

Gravitational waves alternately stretch and squeeze space as they travel along at the speed of light. LIGO was designed to look for these changes by using lasers to monitor the distances between mirrors in a pair of L-shaped antennas in Hanford, Wash., and in Livingston, La. There is another antenna in Italy known as Virgo now undergoing its final testing. When it is online, possibly later this summer (2017), having three detectors will greatly improve astronomers’ ability to tell where the gravitational waves are coming from.

The detectors were designed and built and rebuilt over 40 years to be able to detect collisions of neutron stars—the superdense remnants of some kinds of supernova explosions. Astronomers know such pairs exist in abundance, doomed someday for a fiery ending.

Colliding black holes, being more massive, would be even easier to detect, but LIGO’s founders and funders at the National Science Foundation mostly did not know if there were any around to detect.

Now they know.

The current version of the observatory, known as Advanced LIGO, was still preparing for its first official observing run, in September 2015, when it recorded the collision of a pair of black holes 36 and 29 times as massive as the sun. A second collision, on Dec. 26, 2015, was also confirmed to be massive black holes. A third event in October of that year was probably a black hole merger, the collaboration said.

The burning question now is: Where did such massive black holes come from?

“How were such large black-hole binaries created? How did they form?” Szabolcs Marka, a physics professor at Columbia and LIGO member, said recently. “This is indeed one of the big questions of our field today.”

One possibility is that they were born that way, from a pair of massive stars orbiting each other that evolved, died, blew up and then collapsed again into black holes — all without either star getting kicked out of the system during one of those episodes of stellar violence.

Another idea is that two pre-existing black holes came together by chance and captured each other gravitationally in some crowded part of the galaxy, such as near the center, where black holes might naturally collect.

Astronomers won’t say which explanation is preferred, pending more data, but what Dr. Reitze calls a “tantalizing hint” has emerged from analysis of the Jan. 4 (2017) chirp, namely how the black holes were spinning.

If the stars that gave rise to these black holes had been lifting and evolving together in a binary system, their spins should be aligned, spinning on parallel axes like a pair of gold medal skating dancers at the Olympics, Dr. Reitze explained.

Examination of the January chirp, Dr. Reitze said, gives hints that the spins of the black holes were not aligned, complicating the last motions of their mating dance.

“It was not a simple waltz, it was more like a couple of break dancers,” he said.

As for the original stellar identities of these dark dancers, the consensus, said Daniel Holz of the University of Chicago, is that they were probably very massive and primitive stars at least 40 times heavier than the Sun.

According to theoretical calculations, stars composed of primordial hydrogen and helium and lacking heavier elements like oxygen and carbon, which astronomers with their knack for nomenclature call “metals,” can grow monstrously large. They could collapse directly into black holes when their brief violent lives were over without the benefit of a supernova explosion or other cosmic fireworks.

Dr. Holz said in an email: “It is indeed odd to think that some of the most dramatic stellar collapse do not result in massive stellar explosions outshining galaxies, but instead just involve a star winking out of existence. But that’s what the theory says should happen.”

As if on cue, just last week (June, 2017) astronomers from Ohio State reported that a massive star called N6946-BH1 had suddenly disappeared. The star was in a spiral galaxy 22 million light-years away that is nicknamed the “Fireworks Galaxy” because so many supernova explosions happen in it.

The star, estimated to weigh as much as 25 suns had been brightening since 2009 and was presumably on its way to being a supernova. Instead it winked out in 2015. After a search for remains with the Hubble and Spitzer space telescopes, the astronomers concluded that the supernova had probably fizzled and the star had instead collapsed into a black hole.

In a news release from Ohio State, Kris Stanek, a co-leader of this discovery, said it could help explain the LIGO results and why astronomers didn’t see supernovas from really massive stars. “I suspect it’s much easier to make a very massive black hole if there is no supernova,” he said.

In an email Dr. Stanek wrote, “I am obviously biased, but I think this is a very important discovery, and one that the community is not yet fully ‘groking’ in how it will impact a number of things, including LIGO results.”

Dr. Holz agreed. He said, “We think this might be a channel for ‘heavy’ black hole formation, and it’s amazing to see it actually happening in real time.” Noting that the LIGO observations were in some sense the deaths of the black holes that collided, he added, “so now in some sense we get to watch both the birth and the death of the black holes.”

[1] Dennis Overbye, “Third Gravitational Wave Detection, From Black-Hole Merger 3 Billion Light Years Away ,” New York Times (June 1, 2017). A version of this article appears in print on June 2, 2017, on Page A19 of the New York edition with the headline: “From Cheap Seats on Earth, Sensing a Tiny Echo of a Tumultuous Spectacle.”

All Stars Are Born in Pairs

New Evidence That All Stars Are Born in Pairs[1]

Did our Sun have a twin when it was born 4.5 billion years ago? [Radio image of a very young binary star system, less than about 1 million years old, that formed within a dense core (oval outline) in the Perseus molecular cloud. All stars likely form as binaries within dense cores. SCUBA-2 survey image by Sarah Sadavoy, CfA.]

Almost certainly yes—though not an identical twin. And so did every other sunlike star in the universe, according to a new analysis by a theoretical physicist from the University of California, Berkeley, and a radio astronomer from the Smithsonian Astrophysical Observatory at Harvard University.

Many stars have companions, including our nearest neighbor, Alpha Centauri, a triplet system. Astronomers have long sought an explanation. Are binary and triplet star systems born that way? Did one star capture another? Do binary stars sometimes split up and become single stars?

Astronomers have even searched for a companion to our Sun, a star dubbed Nemesis because it was supposed to have kicked an asteroid into Earth’s orbit that collided with our planet and exterminated the dinosaurs. It has never been found.

The new assertion is based on a radio survey of a giant molecular cloud filled with recently formed stars in the constellation Perseus, and a mathematical model that can explain the Perseus observations only if all sunlike stars are born with a companion.

“We are saying, yes, there probably was a Nemesis, a long time ago,” said co-author Steven Stahler, a UC Berkeley research astronomer.

“We ran a series of statistical models to see if we could account for the relative populations of young single stars and binaries of all separations in the Perseus molecular cloud, and the only model that could reproduce the data was one in which all stars form initially as wide binaries. These systems then either shrink or break apart within a million years.”

In this study, “wide” means that the two stars are separated by more than 500 astronomical units, or AU, where one astronomical unit is the average distance between the Sun and Earth (93 million miles). A wide binary companion to our Sun would have been 17 times farther from the Sun than its most distant planet today, Neptune.

Based on this model, the Sun’s sibling most likely escaped and mixed with all the other stars in our region of the Milky Way galaxy, never to be seen again.

“The idea that many stars form with a companion has been suggested before, but the question is: how many?” said first author Sarah Sadavoy, a NASA Hubble fellow at the Smithsonian Astrophysical Observatory. “Based on our simple model, we say that nearly all stars form with a companion. The Perseus cloud is generally considered a typical low-mass star-forming region, but our model needs to be checked in other clouds.”

The idea that all stars are born in a litter has implications beyond star formation, including the very origins of galaxies, Stahler said.

Astronomers have speculated about the origins of binary and multiple star systems for hundreds of years, and in recent years have created computer simulations of collapsing masses of gas to understand how they condense under gravity into stars. They have also simulated the interaction of many young stars recently freed from their gas clouds. Several years ago, one such computer simulation by Pavel Kroupa of the University of Bonn led him to conclude that all stars are born as binaries.

Yet direct evidence from observations has been scarce. As astronomers look at younger and younger stars, they find a greater proportion of binaries, but why is still a mystery.

“The key here is that no one looked before in a systematic way at the relation of real young stars to the clouds that spawn them,” Stahler said. “Our work is a step forward in understanding both how binaries form and also the role that binaries play in early stellar evolution. We now believe that most stars, which are quite similar to our own Sun, form as binaries. I think we have the strongest evidence to date for such an assertion.”

According to Stahler, astronomers have known for several decades that stars are born inside egg-shaped cocoons called dense cores, which are sprinkled throughout immense clouds of cold, molecular hydrogen that are the nurseries for young stars. Through an optical telescope, these clouds look like holes in the starry sky, because the dust accompanying the gas blocks light from both the stars forming inside and the stars behind. The clouds can, however, be probed by radio telescopes, since the cold dust grains in them emit at these radio wavelengths, and radio waves are not blocked by the dust.

The Perseus molecular cloud is one such stellar nursery, about 600 light-years from Earth and about 50 light-years long. Last year, a team of astronomers completed a survey that used the Very Large Array, a collection of radio dishes in New Mexico, to look at star formation inside the cloud. Called VANDAM, it was the first complete survey of all young stars in a molecular cloud, that is, stars less than about 4 million years old, including both single and multiple stars down to separations of about 15 astronomical units. This captured all multiple stars with a separation of more than about the radius of Uranus’ orbit—19 AU—in our solar system.

Stahler heard about the survey after approaching Sadavoy, a member of the VANDAM team, and asking for her help in observing young stars inside dense cores. The VANDAM survey produced a census of all Class 0 stars–those less than about 500,000 years old–and Class I stars–those between about 500,000 and 1 million years old. Both types of stars are so young that they are not yet burning hydrogen to produce energy.

Sadavoy took the results from VANDAM and combined them with additional observations that reveal the egg-shaped cocoons around the young stars. These additional observations come from the Gould Belt Survey with SCUBA-2 on the James Clerk Maxwell Telescope in Hawaii. By combining these two data sets, Sadavoy was able to produce a robust census of the binary and single-star populations in Perseus, turning up 55 young stars in 24 multiple-star systems, all but five of them binary, and 45 single-star systems.

Using these data, Sadavoy and Stahler discovered that all of the widely separated binary systems–those with stars separated by more than 500 AU–were very young systems, containing two Class 0 stars. These systems also tended to be aligned with the long axis of the egg-shaped dense core. The slightly older Class I binary stars were closer together, many separated by about 200 AU, and showed no tendency to align along the egg’s axis.

“This has not been seen before or tested, and is super interesting,” Sadavoy said. “We don’t yet know quite what it means, but it isn’t random and must say something about the way wide binaries form.”

Stahler and Sadavoy mathematically modeled various scenarios to explain this distribution of stars, assuming typical formation, breakup and orbital shrinking times. They concluded that the only way to explain the observations is to assume that all stars of masses around that of the Sun start off as wide Class 0 binaries in egg-shaped dense cores, after which some 60 percent split up over time. The rest shrink to form tight binaries.

“As the egg contracts, the densest part of the egg will be toward the middle, and that forms two concentrations of density along the middle axis,” he said. “These centers of higher density at some point collapse in on themselves because of their self-gravity to form Class 0 stars.”

“Within our picture, single low-mass, sunlike stars are not primordial,” Stahler added. “They are the result of the breakup of binaries.”

Their theory implies that each dense core, which typically comprises a few solar masses, converts twice as much material into stars as was previously thought.

Stahler said that he has been asking radio astronomers to compare dense cores with their embedded young stars for more than 20 years, in order to test theories of binary star formation. The new data and model are a start, he says, but more work needs to be done to understand the physics behind the rule.

Such studies may come along soon, because the capabilities of a now-upgraded VLA and the ALMA telescope in Chile, plus the SCUBA-2 survey in Hawaii, “are finally giving us the data and statistics we need. This is going to change our understanding of dense cores and the embedded stars within them,” Sadavoy said.

[1] Robert Sanders, “New Evidence That All Stars Are Born in Pairs,” Berkeley News (June 13, 2017)

Nature of Scientific Reasoning

The Nature of Scientific Reasoning[1]

Jacob Bronowski (1908–1974), a Polish-born intellectual, was trained as a mathematician but eventually studied and wrote on the sciences, technology, poetry, the relation between creativity in the arts and the sciences, and man’s attempts to control nature throughout history. A mathematician, a literary critic, a playwright, a scientist, and an acclaimed Renaissance man, Bronowski earned an M.A. degree at Jesus College, Cambridge, England, in 1930, and a Ph.D. in 1933. His extremely wide-ranging career includes lecturing at University College in England; serving as wartime researcher for the British Ministry of Home Security during World War II, when he studied the effects of the atomic bomb; and working at multiple posts at the Salk Institute for Biological Studies in San Diego and posts at Oxford University, Massachusetts Institute of Technology, the University of Rochester, Oregon State University, Yale University, Columbia University, and the National Gallery of Art; and serving as head of projects for the United Nations Educational, Scientific, and Cultural Organization (UNESCO).

Bronowski also worked as a British Broadcasting Corporation (BBC) commentator on atomic energy and other scientific and cultural subjects.

Bronowski came to the United States in 1964. He wrote that, after 1932, he realized it was not enough to work at a desk, was more important and what was defending human decency. It was then that Bronowski turned his attention to studying connections between art and science. Among his writings are: The Poet’s Defence (1939; retitled and reprinted, 1966); a study of William Blake (1943; retitled and reprinted, 1965); Science and Human Values (1965; rev. ed., 1972), his most acclaimed work; and The Ascent of Man (1973), essays based on a BBC television series, his most popular work. Bronowski believed that the progress of science could best be understood by recognizing the interdependence of the sciences, arts, literature, and philosophy. He emphasized the universality of human nature and the need to control violence in modern society.

The Nature of Scientific Reasoning[2]

Jacob Bronowski

What is the insight in which the scientist tries to see into nature? Can it indeed be called either imaginative or creative? To the literary man the question may seem merely silly. He has been taught that science is a large collection of facts; and if this is true, then the only seeing which scientists need to do is, he supposes, seeing the facts. He pictures them, the colorless professionals of science, going off to work in the morning into the universe in a neutral, unexposed state. They then expose themselves like a photographic plate. And then in the darkroom or laboratory they develop the image, so that suddenly and startlingly it appears, printed in capital letters, as a new formula for atomic energy.

Men who have read Balzac and Zola are not deceived by the claims of these writers that they do no more than record the facts. The readers of Christopher Isherwood do not take him literally when he writes “I am a camera.” Yet the same readers solemnly carry with them from their schooldays this foolish picture of the scientist fixing by some mechanical process the facts of nature. I have had of all people a historian tell me that science is a collection of facts, and his voice had not even the ironic rasp of one filing cabinet reproving another.

It seems impossible that this historian had ever studied the beginnings of a scientific discovery. The Scientific Revolution can be held to begin in the year 1543 when there was brought to Copernicus, perhaps on his deathbed, the first printed copy of the book he had finished about a dozen years earlier. The thesis of this book is that Earth moves around the Sun. When did Copernicus go out and record this fact with his camera? What appearance in nature prompted his outrageous guess? And in what odd sense is this guess to be called a neutral record of fact?

Less than a hundred years after Copernicus, Kepler published (between 1609 and 1619) the three laws which describe the paths of the planets. The work of Newton and with it most of our mechanics spring from these laws. They have a solid, matter-of-fact sound. For example, Kepler says that if one squares the year of a planet, one gets a number which is proportional to the cube of its average distance from the Sun. Does anyone think that such a law is found by taking enough readings and then squaring and cubing everything in sight? If he does, then, as a scientist, he is doomed to a wasted life; he has as little prospect of making a scientific discovery as an electronic brain has.

It was not this way that Copernicus and Kepler thought, or that scientists think today. Copernicus found that the orbits of the planets would look simpler if they were looked at from the Sun and not from Earth. But he did not in the first place find this by routine calculation. His first step was a leap of imagination—to lift himself from Earth, and put himself wildly, speculatively into the Sun. “Earth conceives from the Sun,” he wrote; and “the Sun rules the family of stars.” We catch in his mind an image, the gesture of the virile man standing in the Sun, with arms out-stretched, overlooking the planets. Perhaps Copernicus took the picture from the drawings of the youth with outstretched arms which the Renaissance teachers put into their books on the proportions of the body. Perhaps he had seen Leonardo’s drawings of his loved pupil Salai. I do not know. To me, the gesture of Copernicus, the shining youth looking outward from the Sun, is still vivid in a drawing which William Blake in 1780 based on all these: the drawing which is usually called Glad Day.

Kepler’s mind, we know, was filled with just such fanciful analogies; and we know that they were. Kepler wanted to relate the speeds of the planets to the musical intervals. He tried to fit the five regular solids into their orbits. None of these likenesses worked, and they have been forgotten; yet they have been and they remain the stepping stones of every creative mind. Kepler felt for his laws by way of metaphors, he searched mystically for likenesses with what he knew in every strange corner of nature. And when among these guesses he hit upon his laws, he did not think of their numbers as the balancing of a cosmic bank account, but as a revelation of the unity in all nature. To us, the analogies by which Kepler listened for the movement of the planets in the music of the spheres are farfetched. Yet are they more so than the wild leap by which Rutherford and Bohr in our own century found a model for the atom in, of all places, the planetary system?

No scientific theory is a collection of facts. It will not even do to call a theory true or false in the simple sense in which every fact is either so or not so. The Epicureans held that matter is made of atoms 2000 years ago and we are now tempted to say that their theory was true. But if we do so we confuse their notion of matter with our own. John Dalton in 1808 first saw the structure of matter as we do today, and what he took from the ancients was not their theory but something richer, their image: the atom. Much of what was in Dalton’s mind was as vague as the Greek notion, and quite as mistaken. But he suddenly gave life to the new facts of chemistry and the ancient theory together, by fusing them to give what neither had: a coherent picture of how matter is linked and built up from different kinds of atoms. The act of fusion is the creative act.

All science is the search for unity in hidden likenesses. The search may be on a grand scale, as in the modern theories which try to link the fields of gravitation and electromagnetism. But we do not need to be browbeaten by the scale of science. There are discoveries to be made by snatching a small likeness from the air too, if it is bold enough. In 1935 the Japanese physicist Hideki Yukawa wrote a paper which can still give heart to a young scientist. He took as his starting point the known fact that waves of light can sometimes behave as if they were separate pellets. From this he reasoned that the forces which hold the nucleus of an atom together might sometimes also be observed as if they were solid pellets. A schoolboy can see how thin Yukawa’s analogy is, and his teacher would be severe with it. Yet Yukawa without a blush calculated the mass of the pellet he expected to see, and waited. He was right; his meson was found, and a range of other mesons, neither the existence nor the nature of which had been suspected before. The likeness had borne fruit.

The scientist looks for order in the appearances of nature by exploring such like- nesses. For order does not display itself of itself; if it can be said to be there at all, it is not there for the mere looking. There is no way of pointing a finger or camera at it; order must be discovered and, in a deep sense, it must be created. What we see, as we see it, is mere disorder.

This point has been put trenchantly in a fable by Karl Popper. Suppose that someone wishes to give his whole life to science. Suppose that he therefore sat down, pencil in hand, and for the next twenty, thirty, forty years recorded in notebook after notebook everything that he could observe. He may be supposed to leave out nothing: today’s humidity, the racing results, the level of cosmic radiation and the stock-market prices and the look of Mars, all would be there. He would have compiled the most careful record of nature that has ever been made; and, dying in the calm certainty of a life well spent, he would of course leave his notebooks to the Royal Society. Would the Royal Society thank him for the treasure of a lifetime of observation? It would not. The Royal Society would treat his notebooks exactly as the English bishops have treated Joanna Southcott’s box. It would refuse to open them at all, because it would know without looking that the notebooks contain only a jumble of disorderly and meaningless items.

Science finds order and meaning in our experience, and sets about this in quite a different way. It sets about it as Newton did in the story which he himself told in his old age, and of which the schoolbooks give only a caricature. In the year 1665, when Newton was 22, the plague broke out in southern England, and the University of Cambridge was closed. Newton therefore spent the next 18 months at home, removed from traditional learning, at a time when he was impatient for knowledge and, in his own phrase, “I was in the prime of my age for invention.” In this eager, boyish mood, sitting one day in the garden of his widowed mother, he saw an apple fall. So far the books have the story right; we think we even know the kind of apple; tradition has it that it was a Flower of Kent. But now they miss the crux of the story. For what struck the young Newton at the sight was not the thought that the apple must be drawn to Earth by gravity; that conception was older than Newton. What struck him was the conjecture that the same force of gravity, which reaches to the top of the tree, might go on reaching out beyond Earth and its air, endlessly into space. Gravity might reach the moon: this was Newton’s new thought; and it might be gravity which holds the Moon in her orbit. There and then he calculated what force from Earth (falling off as the square of the distance) would hold the Moon, and compared it with the known force of gravity at tree height. The forces agreed; Newton says laconically, “I found them answer pretty nearly.” Yet they agreed only nearly: the likeness and the approximation go together, for no likeness is exact. In Newton’s science modern sciences is full grown.

It grows from a comparison. It has seized a likeness between two unlike appear- ances; for the apple in the summer garden and the grave moon overhead are surely as unlike in their movements as two things can be. Newton traced in them two expres- sions of a single concept, gravitation: and the concept (and the unity) are in that sense his free creation. The progress of science is the discovery at each step of a new order which gives unity to what had long seemed unlike.

Questions for Discussion

  1. What is scientific reasoning? How does it differ from other kinds of reasoning?
  2. Where does the erroneous image of scientists as merely reporting facts come from?
  3. If science is not “a collection of facts” (Paragraph 2), what is it? Why can science not be just a collection of facts? What is a “fact”?
  4. How do new scientific theories develop? How are old ideas transformed into new ones?
  5. What is the purpose of science?
  6. Why can good science never be purely objective? Why will pure objectivity not work? In what way should scientists be subjective?
  7. Bronowski says in Paragraph 8, “All science is the search for unity in hidden likenesses.” What examples does he include to illustrate that statement? What does that statement mean?

Questions for Reflection and Writing

  1. Describe the process by which scientists think. Consider Copernicus and Kepler: What were their processes? How does their way of thinking still describe how scientists think today?
  2. Define a type of reasoning, besides scientific, with which you are familiar. Examples might include artistic reasoning, intuitive reasoning, and historical reasoning. Describe the thinking process, providing examples from your experience, and explain how this process works.
  3. Look up Leonardo da Vinci’s drawing of the proportions of the body and William Blake’s Glad Day, mentioned in Paragraph 5. Write an essay in which you explain how these drawings illustrate scientific thought. Other artworks on scientific topics could also be used in your essay.

[1] From http://www.public.iastate.edu/~bccorey/105%20Folder/The%20Nature%20of%20Sci.pdf.

[2] Copyright © 1956 by Jacob Bronowski. Copyright renewed 1984 by Rita Bronowski.