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)

Dying Stars and Black Holes

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)

Forming a Black Hole

Forming a Black Hole[1]

On July 2, 1967, a network of satellites designed to detect tests of nuclear weapons recorded a flash of gamma rays coming from the wrong direction—outer space.

And so it was that human astronomers were tipped to the existence of one of the most violent phenomena of nature. Today, they know that about once a day somewhere in the observable universe, an explosion called a gamma-ray burst occurs, releasing more energy in a few seconds than our galaxy does in a year.

These magnificent cosmic conflagrations are as far away as they are rare, which is just as well. If one happened nearby, in our own galaxy, we could be swathed with radiation. The closest gamma-ray burst whose distance has been measured happened some 119 million light-years from us, far outside the so-called Local Group, which contains our own Milky Way galaxy. The farthest so far recorded is now 31 billion light-years away, as calculated by the mathematics of the expanding universe; it happened when the universe was only 500 million years old.

Gamma-ray bursts are thought to be the final step in the series of transformations by which stars shrink and slump from blazing glory to oblivion, winding up as bottomless deadly dimples in the fabric of space-time—that is to say, as black holes.

The hierarchy of dead stars goes like this: Stars like the Sun, when they run out of thermonuclear fuel, shrink to cinders known as white dwarfs, the size of Earth. Stars more massive than the Sun might collapse more drastically and undergo a supernova explosion, blasting newly formed heavy elements into space to enrich future stars, planets and perhaps life, and leaving behind crushed cores known as neutron stars. These weigh slightly more than the sun but are only 12 miles or so in diameter—so dense that a teaspoonful on Earth would weigh as much as Mount Everest.

Such an explosion, bright enough to be seen in daylight, happened in 1054, Earth time, as told by Chinese astronomers and the ancient inhabitants of Chaco Canyon in what is now New Mexico. That supernova left behind the Crab nebula, a tangle of glowing shreds of gas and a pulsar—a magnetized neutron star spinning 30 times a second, whipping the gas with magnetic fields that make it glow.

Neutron stars, theorists say, are the densest stable form of matter, but they are not the end of the story. According to theory, too much mass accumulating on a neutron star can cause its collapse into a black hole, an abyss from which not even light can escape. The signature of such a cataclysm would be a gamma-ray burst, astronomers say.

Supercomputer simulations by astronomers led by Luciano Rezzolla of the Institute of Theoretical Physics in Frankfurt have recently showed this would work.

The simulation, as it unwound over six weeks of supercomputer time at the Max Planck Institute for Gravitational Physics, started with two neutron stars orbiting each other at a distance of 11 miles. That would not be unusual in the universe; most stars are in fact part of double-star systems and several pairs of pulsars orbiting each other are already known. They will eventually collide because such dense, heavy objects lose energy rapidly and spiral together.

In the case of Dr. Rezzolla’s computation, it took seven milliseconds for tidal forces from the larger star’s gravity to rip apart the smaller star and unwind it into a spiral resembling flaming toothpaste writhing with magnetic fields and begin munching up the gas.

The excess plasma forms a fat disk around the new black hole, and its magnetic fields, a billion times stronger than those in the Sun, align to channel beams of radiation and particles out at the speed of light. The result is a gamma-ray burst visible across the universe, carrying the news of doom—the last astronomers will ever hear of these stars.

For those two stars, the last bang was the best. Oblivion can be such a lovely sight.

[1] Dennis Overbye, “How to Make a Black Hole,” New York Times (October 8, 2014). The graphic is from Astronews in Astronomy (45, 7, July 2017), p 15

This Black Hole is too Bright

This Black Hole is too Bright[1]

The extreme gravity of a black hole attracts nearby material, funneling it into what’s called an accretion disk. Friction among gas particles within the disk causes it to glow across a range of wavelengths. When this emitted radiation balances the inward gravitational pull, astronomers say the black hole has reached the Eddington limit. Because each black hole’s limit depends on its mass, they have a way to measure the black hole’s mass.

After studying the light output of an ultraluminous x-ray source in spiral galaxy M101, called M101 ULX-1, researchers thought the source was a black hole between 100 and 1,000 times the Sun’s mass. However, observations and the following analysis reported in November 28 issue of Nature (See “Puzzling accretion onto a black hole in the ultraluminous x-ray source M 101 ULX-1, Nature 503, November 28, 2013), pp. 500-503) suggest instead that the black hole is between 20 and 30 solar masses.

Ji-Feng Liu of the Chinese Academy of Sciences in Beijing and colleagues come to this conclusion after studying M101 ULX-1’s spectrum, which plots the detected brightness of each wavelength. From that , they learned that the black hole’s companion— the object that donates material to the accretion disk—is a Wolf-Rayet star with 19 solar masses. A wind of particles and radiation lows from the star and likely feeds the black hole’s accretion disk. The team also determined that the two complete a full rotation around each other in 8.2 days. From those two pieces of information, Liu’s team calculated the mass of the black hole: 20-30 times the Sun.

This stellar-mass black hole is much more energetic than it should be given its mass; the astronomers refer to the object as having super-Eddington luminosity. “These findings show that our understanding of black hole accretion is incomplete and needs revision,” says Liu.

[1] See “Astronews,” Astronomy (42, 3, March 2014, p. 14)

Runaway Black Hole Flees a Huge Galaxy

Runaway Black Hole Flees a Huge Galaxy

It’s tempting to think of black holes as monsters, especially the supermassive variety. These beasts lurk at the centers of most galaxies and can be millions or even billions of times more massive than the Sun. When they eat, they feast—gobbling down gas then flinging radio-emitting jets out into intergalactic space.

So it’s a little odd that such a monster might be spotted running away, but that’s just what astronomers have found. In a recent search of nearby galaxies, Jim Condon (NRAO) and colleagues came upon a supermassive black hole stripped of most of its galaxy and fleeing from a big “Jabba the Hut”-type elliptical. The results have been accepted for publication in the Astrophysical Journal.

Condon started out trying to find supermassive black holes that didn’t live right in the centers of their galaxies. Galaxies are thought to grow in part by mergers with other galaxies. If that’s the case, the two black holes at the center of each galaxy would also have to unite, and that process might deliver a good kick to the resulting, larger black hole, shooting it off-center. Condon surveyed hundreds of nearby galaxies searching for this expected signature of galaxy mergers.

He didn’t find any. What he did find was even weirder — a galaxy on the run.

About 30,000 light-years from a brilliant, massive elliptical galaxy shone a surprisingly luminous source of radio waves. The source was too bright to be anything other than an accreting supermassive black hole. Yet it was much too far from the galaxy’s core to belong to it.

Condon and colleagues followed up with Hubble and Spitzer observations for a closer look. To their surprise, they found that the radio source sat in its own little galaxy, which has the mass of some 6 billion Suns—less than 1% of the Milky Way’s mass and atypically tiny to be hosting a supermassive black hole.

Hubble images also revealed a trail of ionized gas extending from the tiny galaxy to its much bigger sibling. The trail (and specific wavelengths of light that the trail emits) shows that the little galaxy is speeding away from the larger one at more than 2,000 kilometers per second (4.5 million mph). Whether it remains gravitationally bound or is heading out of the cluster toward intercluster space isn’t yet known.

So what happened to this odd little galaxy? The scenario Condon’s team finds most likely is that the speedy galaxy was once a normal galaxy that fell into the gravitational well around the “Jabba the Hut” elliptical at the cluster’s center. It came very close to being destroyed, passing within 3,000 light-years of the elliptical’s core, but it managed to come out the other side of its slingshot pass. As it passed, gravitational tidal forces stripped away most of the galaxy’s stars and gas, but the very core of the galaxy — and its supermassive black hole — survived.

So now what? What’s left of the galaxy is still trailing debris and will eventually cease star formation. The supermassive black hole at its center may speed this process along if its radiation helps push gas out. In a billion years or so, the black hole probably will be invisible, wandering undetected through intergalactic space.

Watch Jim Condon explain the find:

http://www.skyandtelescope.com/astronomy-news/black-hole-flees-behemoth-galaxy/

Anatomy of a Black Hole

Anatomy of a Black Hole[1]

A black hole is a pit in the fabric of spacetime. Space and time, according to Einstein’s theory of special relativity, are interchangeable parts of a thing called space-time: much as width, height, and depth are dimensions of a box, so space and time are dimensions of spacetime. Although the dimensions of space and time are relative and can change, contracting or dilating depending on your frame of reference—an effect noticeable when dealing with strong gravity or relativistic speeds—units of spacetime are absolute.

The figure above gives a cursory explanation and overview of what a black hole actually is. Not only is it a singularity, but it spins. Fast! When astronomers measure a black hole’s spin, they report the value as a fraction of the maximum allowed spin (which would be 1). The bigger member of the black hole binary in the quasar OJ 287 has a spin, labeled OJ 287 has a spin, labeled a, of 0.313, or 31.3% of its max,. What does that mean? This number is related to the angular momentum; it’s not a fraction of the speed of light. But we can turn it into a fraction of the speed of light. That is given (after some messy algebra)

We are pretty sure that black holes really do exist. Stars and gas at the centers of many galaxies orbit around invisible but incredibly massive objects, and we can tell how massive the object is based on these orbits: millions to billions of Suns’ worth of mass. Could it be that we don’t really understand gravity, and something else explains black holes? Yes, but no other ideas have worked out.

[1] Camille M. Carlisle, “Anatomy of a Black Hole,? Sky and Telescope (133, 2, February , 2017), pp. 16-17