Science Current Events | Science News | Brightsurf.com
 

How black holes grow

April 02, 2012
New study indicates they eat binary star partners

SALT LAKE CITY -- A study led by a University of Utah astrophysicist found a new explanation for the growth of supermassive black holes in the center of most galaxies: they repeatedly capture and swallow single stars from pairs of stars that wander too close.

Using new calculations and previous observations of our own Milky Way and other galaxies, "we found black holes grow enormously as a result of sucking in captured binary star partners," says physics and astronomy Professor Ben Bromley, lead author of the study, which is set for online publication April 2 in Astrophysical Journal Letters.

"I believe this has got to be the dominant method for growing supermassive black holes," he adds. "There are two ways to grow a supermassive black hole: with gas clouds and with stars. Sometimes there's gas and sometimes there is not. We know that from observations of other galaxies. But there are always stars."

"Our mechanism is an efficient way to bring a star to a black hole," Bromley says. "It's really hard to target a single star at a black hole. It's a lot easier to throw a binary at it," just as it's more difficult to hit a target using a slingshot, which hurls a single stone, than with a bola, which hurls two weights connected by a cord.

A binary pair of stars orbiting each other "is essentially a single object much bigger than the size of the individual stars, so it is going to interact with the black hole more efficiently," he explains. "The binary doesn't have to get nearly as close for one of the stars to get ripped away and captured."

But to prove the theory will require more powerful telescopes to find three key signs: large numbers of small stars captured near supermassive black holes, more observations of stars being "shredded" by gravity from black holes, and large numbers of "hypervelocity stars" that are flung from galaxies at more than 1 million mph when their binary partners are captured.

Bromley, a University of Utah astrophysicist, did the study with astronomers Scott Kenyon, Margaret Geller and Warren Brown, all of the Smithsonian Astrophysical Observatory in Cambridge, Mass. The study was funded by both institutions.

What Does a Supermassive Black Hole Eat: Gas or Stars?

Black holes are objects in space so dense that not even light can escape their gravity, although powerful jets of light and energy can be emitted from a black hole's vicinity as gas and stars are sucked into it.

Small black holes result from the collapse of individual stars. But the centers of most galaxies, including our own Milky Way, are occupied by what are popularly known as "supermassive" black holes that contain mass ranging from 1 million to 10 billion stars the size of our sun.

Astrophysicists long have debated how supermassive black holes grew during the 14 billion years since the universe began in a great expansion of matter and energy named the Big Bang. One side believes black holes grow larger mainly by sucking in vast amounts of gas; the other side says they grow primarily by capturing and sucking in stars.

Just last month, other researchers published a theory that a black hole sucks in "food" by tipping its "plates" - two tilted gas disks colliding as they orbit the black hole - in a way that makes the speeding gas slow down so the black hole can swallow it.

Bromley says that theory overcomes a key problem: gas flows into black holes inefficiently. "But are misaligned gas disks common enough to be important for black hole growth?" he asks. "It's fair to say that gas contributes to the growth of black holes, but it is still uncertain how."

The new theory about binary stars - a pair of stars that orbit each other - arose from Bromley's earlier research to explain hypervelocity stars, which have been observed leaving our Milky Way galaxy at speeds ranging from 1.1 million to 1.8 million mph, compared with the roughly 350,000 mph speed of most stars.

Munching Binaries: One is Captured, One Speeds Away

"The hypervelocity stars we see come from binary stars that stray close to the galaxy's massive black hole," he says. "The hole peels off one binary partner, while the other partner - the hypervelocity star - gets flung out in a gravitational slingshot."

"We put the numbers together for observed hypervelocity stars and other evidence, and found that the rate of binary encounters [with our galaxy's supermassive black hole] would mean most of the mass of the galaxy's black hole came from binary stars," Bromley says. "We estimated these interactions for supermassive black holes in other galaxies and found that they too can grow to billions of solar masses in this way."

As many as half of all stars are in binary pairs, so they are plentiful in the Milky Way and other galaxies, he adds. But the study assumed conservatively that only 10 percent of stars exist in binary pairs.

The new study looked at each step in the process of a supermassive black hole eating binary stars, and calculated what would be required for the process to work in terms of the rates at which hypervelocity stars are produced, binary partners are captured, the captured stars are bound to the black hole in elongated orbits and then sucked into it.

The scientists then compared the results with actual observations of supermassive black holes, stars clustering near them and "tidal disruption events" in which black holes in other galaxies are seen to shred stars while pulling them into the hole.

"It fits together, and it works," Bromley says. "When we look at observations of how stars are accumulating in our galactic center, it's clear that much of the mass of the black hole likely came from binary stars that were torn apart."

He refers to the process of a supermassive black hole capturing stars from binary pairs as "filling the bathtub." Once the tub - the area near the black hole - is occupied by a cluster of captured stars, they go "down the drain" into the black hole over millions of years. His study shows the "tub" fills at about the same rate it drains, meaning stars captured by a supermassive black hole eventually are swallowed.

The study's key conclusions:

-- The theory accurately predicts the rate (one every 1,000 to 100,000 years) at which hypervelocity stars are observed leaving our galaxy and at which stars are captured into the star cluster seen near our galaxy's supermassive black hole.

-- The rate of "tidal disruption events," which are stars being shredded and pulled into supermassive black holes in other galaxies, also matches what the theory predicts, based on the limited number seen since they first were observed in the early 2000s. That rate also is one every 1,000 to 100,000 years.

-- The calculations show how the theory's rate of binary capture and consumption can explain how the Milky Way's supermassive black hole has at least doubled to quadrupled in mass during the past 5 billion to 10 billion years.

When the researchers considered the number of stars near the Milky Way's center, their speed and the odds they will encounter the supermassive black hole, they estimated that one binary star will be torn apart every 1,000 years by the hole's gravity.

During the last 10 billion years, that would mean the Milky Way's supermassive black hole ate 10 million solar masses - more than enough to account for the hole's actual size of 4 million solar masses.

"We found a wide range of black hole masses can be explained by this process," Bromley says.

Confirmation of the theory must await more powerful orbiting and ground-based telescopes. To confirm the theory, such telescopes should find many more stars in the cluster near the Milky Way's supermassive black hole (we now see only the brightest ones), a certain rate of hypervelocity stars in southern skies, and more observations of stars being shredded in other galaxies.

University of Utah


Related Supermassive Black Hole Current Events and Supermassive Black Hole News Articles


Supermassive black hole blows molecular gas out of galaxy at 1 million kilometers per hour
New research by academics at the University of Sheffield has solved a long-standing mystery surrounding the evolution of galaxies, deepening our understanding of the future of the Milky Way.

A hotspot for powerful cosmic rays
An observatory run by the University of Utah found a "hotspot" beneath the Big Dipper emitting a disproportionate number of the highest-energy cosmic rays. The discovery moves physics another step toward identifying the mysterious sources of the most energetic particles in the universe.

Swiftly moving gas streamer eclipses supermassive black hole
An international team of astronomers has discovered that the supermassive black hole at the heart of the galaxy NGC 5548 has recently undergone strange, unexpected behavior rarely seen in the heart of active galaxies.

Astronomers pierce galactic clouds to shine light on black hole development
An international team of scientists including a Virginia Tech physicist have discovered that winds blowing from a supermassive black hole in a nearby galaxy work to obscure observations and x-rays.

Swiftly moving gas streamer eclipses supermassive black hole
Astronomers have discovered strange and unexpected behaviour around the supermassive black hole at the heart of the galaxy NGC 5548.

Swiftly Moving Gas Streamer Eclipses Supermassive Black Hole
An international team of astronomers, using data from several NASA and European Space Agency (ESA) space observatories, has discovered unexpected behavior from the supermassive black hole at the heart of the galaxy NGC 5548, located 244.6 million light-years from Earth.

Nearest bright 'hypervelocity star' found
A University of Utah-led team discovered a "hypervelocity star" that is the closest, second-brightest and among the largest of 20 found so far.

Georgia Tech researchers use XSEDE supercomputers to understand and predict how black holes swallow stars
Somewhere in the cosmos an ordinary galaxy spins, seemingly at slumber. Then all of a sudden, WHAM! A flash of light explodes from the galaxy's center. A star orbiting too close to the event horizon of the galaxy's central supermassive black hole is torn apart by the force of gravity, heating up its gas and sending out a beacon to the far reaches of the universe.

Watching for a black hole to gobble up a gas cloud
Right now a doomed gas cloud is edging ever closer to the supermassive black hole at the center of our Milky Way galaxy. These black holes feed on gas and dust all the time, but astronomers rarely get to see mealtime in action.

RXTE Reveals the Cloudy Cores of Active Galaxies
Picture a single cloud large enough to span the solar system from the sun to beyond Pluto's orbit. Now imagine many such clouds orbiting in a vast ring at the heart of a distant galaxy, occasionally dimming the X-ray light produced by the galaxy's monster black hole.
More Supermassive Black Hole Current Events and Supermassive Black Hole News Articles

Black Holes! Learn About Black Holes and Enjoy Colorful Pictures - Look and Learn! (50+ Photos of Black Holes)

Black Holes! Learn About Black Holes and Enjoy Colorful Pictures - Look and Learn! (50+ Photos of Black Holes)


Are your kids interested in Black Holes? Awesome! You have found the right book. Help your children learn more about Black Holes today by reading this book.

Here is what is included inside "Black Holes! Learn About Black Holes and Enjoy Colorful Pictures – Look and Learn!"...

Black Holes
Space
Rogue Black Holes
Black Hole Images
Black Hole Facts
Supermassive Black Holes
Black Hole Structures
Event Horizons
Singularities
Fun Black Hole Facts
And Lots More!

Includes over 50 high quality photos of Black Holes!

Other bonuses inside "Black Holes! Learn About Black Holes and Enjoy Colorful Pictures – Look and Learn!"...
This book has photos of Black Holes.
This...

Death by Black Hole: And Other Cosmic Quandaries

Death by Black Hole: And Other Cosmic Quandaries
by Neil deGrasse Tyson (Author)


A vibrant collection of essays on the cosmos from the nation's best-known astrophysicist. “One of today’s best popularizers of science.”—Kirkus Reviews. Loyal readers of the monthly "Universe" essays in Natural History magazine have long recognized Neil deGrasse Tyson's talent for guiding them through the mysteries of the cosmos with clarity and enthusiasm. Bringing together more than forty of Tyson's favorite essays, ?Death by Black Hole? explores a myriad of cosmic topics, from what it would be like to be inside a black hole to the movie industry's feeble efforts to get its night skies right. One of America's best-known astrophysicists, Tyson is a natural teacher who simplifies the complexities of astrophysics while sharing his infectious fascination for our...

The Galactic Supermassive Black Hole

The Galactic Supermassive Black Hole
by Fulvio Melia (Author)


Here, one of the world's leading astrophysicists provides the first comprehensive and logically structured overview of the many ideas and discoveries pertaining to the supermassive black hole at the galactic center known as Sagittarius A*. By far the closest galactic nucleus in the universe, Sagittarius A* alone can provide us with a realistic expectation of learning about the physics of strong gravitational fields, and the impact of such fields on the behavior of matter and radiation under severe physical conditions. Its proximity may even provide the opportunity to directly test one of general relativity's most enigmatic predictions--the existence of closed pockets of space-time hidden behind an event horizon. The plethora of research on Sagittarius A* since its discovery in 1974 has...

Black Holes : Just Facts For Kids

Black Holes : Just Facts For Kids


This is an educational children's picture book with plenty of facts to expand young minds. Sara Myers simply explains how black holes come in to existence without using overly complicated words or phrases.

Children will learn about:

* Mass
* How mass and gravity are linked
* Where black holes come from
* The event horizon and why you can't see inside a black hole

The fantastic pictures are sure to fire your child's imagination, and keep them interested all the way through.

This book is suitable for any children with an interest in space and science, and all the complex ideas are presented very simply.

Black Holes, White Dwarfs and Neutron Stars: The Physics of Compact Objects

Black Holes, White Dwarfs and Neutron Stars: The Physics of Compact Objects
by Stuart L. Shapiro (Author), Saul A. Teukolsky (Author)


This self-contained textbook brings together many different branches of physics--e.g. nuclear physics, solid state physics, particle physics, hydrodynamics, relativity--to analyze compact objects. The latest astronomical data is assessed. Over 250 exercises.

Black Holes And Beyond: An Introduction

Black Holes And Beyond: An Introduction
by Werner Brueckner (Author)


The reader will experience the latest state of knowledge, including the newest discovery of a black hole in the centre of the Milky Way. The book is for future students of science subjects and also for those simply interested in Astronomy and Astrophysics. It is specifically an introduction to this fascinating subject, with the intention of providing a very wide overview assisted by many illustrations, putting it ahead of similar books but without going too deeply into the details.

Dinosauria - Part VII: Supermassive Black Hole

Dinosauria - Part VII: Supermassive Black Hole
by Vox Populi


Following the events of Dinosauria - Part VI: Purple...Andie Lee Vibert is alone on Thoth. Her friends are all either missing or disappeared after the Saurian raid. She thinks her part in things is done...until she makes a discovery...a message left behind by Andrea-her time twin-a message that suggests that Jack is in danger, and that she may be the only one who can save him...and the universe.

The Edge of Infinity: Supermassive Black Holes in the Universe

The Edge of Infinity: Supermassive Black Holes in the Universe
by Fulvio Melia (Author)


This timely book is suitable for the general reader wishing to find answers to some of the intriguing questions now being asked about black holes. Although once recognized as the most destructive force in nature, following a cascade of astonishing discoveries, the opinion of supermassive black holes has undergone a dramatic shift. Astronomers are discovering that these objects may have been critical to the formation of structure in the early universe, spawning bursts of star formation, planets, and even life itself. Fulvio Melia is Associate Head of Physics and Professor of Astronomy at the University of Arizona. He is author of Electrodynamics (University of Chicago, 2001), and a forthcoming title, The Black Hole at the Center of Our Galaxy (Princeton).

The Black Hole at the Center of Our Galaxy

The Black Hole at the Center of Our Galaxy
by Fulvio Melia (Author)


Could Einstein have possibly anticipated directly testing the most captivating prediction of general relativity, that there exist isolated pockets of spacetime shielded completely from our own? Now, almost a century after that theory emerged, one of the world's leading astrophysicists presents a wealth of recent evidence that just such an entity, with a mass of about three million suns, is indeed lurking at the center of our galaxy, the Milky Way--in the form of a supermassive ''black hole''! With this superbly illustrated, elegantly written, nontechnical account of the most enigmatic astronomical object yet observed, Fulvio Melia captures all the excitement of the growing realization that we are on the verge of actually seeing this exotic object within the next few years. Melia traces...

Measuring the Angular Momentum of Supermassive Black Holes (SpringerBriefs in Astronomy)

Measuring the Angular Momentum of Supermassive Black Holes (SpringerBriefs in Astronomy)
by Laura Brenneman (Author)


Measuring the spin distribution of supermassive black holes is of critical importance for understanding how these black holes and their host galaxies form and evolve over time, yet this type of study is only in its infancy.  This brief describes how astronomers measure spin in supermassive black holes using X-ray spectroscopy.   It also reviews the constraints that have been placed on the spin distribution in local, bright active galaxies over the past six years, and the cosmological implications of these constraints.  Finally, it summarizes the open questions that remain in this exciting new field of research and points toward future discoveries soon to be made by the next generation of space-based observatories.

© 2014 BrightSurf.com