Early Supermassive Black Holes First Formed as Twins

It’s one of the puzzles of cosmology and stellar evolution: how did supermassive black holes get so… well, supermassive… in the early Universe, when seemingly not enough time had yet passed for them to accumulate their mass through steady accretion processes alone? It takes a while to eat up a billion solar masses’ worth of matter, even with a healthy appetite and lots within gravitational reach. But yet there they are: monster black holes are common within some of the most distant galaxies, flaunting their precocious growth even as the Universe was just celebrating its one billionth birthday.

Now, recent findings by researchers at Caltech suggest that these ancient SMBs were formed by the death of certain types of primordial giant stars, exotic stellar dinosaurs that grew large and died young. During their violent collapse not just one but two black holes are formed, each gathering its own mass before eventually combining together into a single supermassive monster.

Watch a simulation and find out more about how this happens below:

From a Caltech news article by Jessica Stoller-Conrad:

To investigate the origins of young supermassive black holes, Christian Reisswig, NASA Einstein Postdoctoral Fellow in Astrophysics at Caltech and Christian Ott, assistant professor of theoretical astrophysics, turned to a model involving supermassive stars. These giant, rather exotic stars are hypothesized to have existed for just a brief time in the early Universe.

Read more: How Do Black Holes Get Super Massive?

Unlike ordinary stars, supermassive stars are stabilized against gravity mostly by their own photon radiation. In a very massive star, photon radiation—the outward flux of photons that is generated due to the star’s very high interior temperatures—pushes gas from the star outward in opposition to the gravitational force that pulls the gas back in.

During its life, a supermassive star slowly cools due to energy loss through the emission of photon radiation. As the star cools, it becomes more compact, and its central density slowly increases. This process lasts for a couple of million years until the star has reached sufficient compactness for gravitational instability to set in and for the star to start collapsing gravitationally.

Previous studies predicted that when supermassive stars collapse, they maintain a spherical shape that possibly becomes flattened due to rapid rotation. This shape is called an axisymmetric configuration. Incorporating the fact that very rapidly spinning stars are prone to tiny perturbations, Reisswig and his colleagues predicted that these perturbations could cause the stars to deviate into non-axisymmetric shapes during the collapse. Such initially tiny perturbations would grow rapidly, ultimately causing the gas inside the collapsing star to clump and to form high-density fragments.

“The growth of black holes to supermassive scales in the young universe seems only possible if the ‘seed’ mass of the collapsing object was already sufficiently large.”

– Christian Reisswig, NASA Einstein Postdoctoral Fellow at Caltech

Composite image from Chandra and Hubble showing supermassive black holes in the early Universe.
Composite image from Chandra and Hubble showing supermassive black holes in the early Universe.

These fragments would orbit the center of the star and become increasingly dense as they picked up matter during the collapse; they would also increase in temperature. And then, Reisswig says, “an interesting effect kicks in.” At sufficiently high temperatures, there would be enough energy available to match up electrons and their antiparticles, or positrons, into what are known as electron-positron pairs. The creation of electron-positron pairs would cause a loss of pressure, further accelerating the collapse; as a result, the two orbiting fragments would ultimately become so dense that a black hole could form at each clump. The pair of black holes might then spiral around one another before merging to become one large black hole.

“This is a new finding,” Reisswig says. “Nobody has ever predicted that a single collapsing star could produce a pair of black holes that then merge.”

These findings were published in Physical Review Letters the week of October 11. Source: Caltech news article by Jessica Stoller-Conrad.

Supermassive Black Holes Keep Galaxies From Getting Bigger

It’s long been a mystery for astronomers: why aren’t galaxies bigger? What regulates their rates of star formation and keeps them from just becoming even more chock-full-of-stars than they already are? Now, using a worldwide network of radio telescopes, researchers have observed one of the processes that was on the short list of suspects: one supermassive black hole’s jets are plowing huge amounts of potential star-stuff clear out of its galaxy.

Astronomers have theorized that many galaxies should be more massive and have more stars than is actually the case. Scientists proposed two major mechanisms that would slow or halt the process of mass growth and star formation — violent stellar winds from bursts of star formation and pushback from the jets powered by the galaxy’s central, supermassive black hole.

Read more: Our Galaxy’s Supermassive Black Hole is a Sloppy Eater

“With the finely-detailed images provided by an intercontinental combination of radio telescopes, we have been able to see massive clumps of cold gas being pushed away from the galaxy’s center by the black-hole-powered jets,” said Raffaella Morganti, of the Netherlands Institute for Radio Astronomy and the University of Groningen.

The scientists studied a galaxy called 4C12.50, nearly 1.5 billion light-years from Earth. They chose this galaxy because it is at a stage where the black-hole “engine” that produces the jets is just turning on. As the black hole, a concentration of mass so dense that not even light can escape, pulls material toward it, the material forms a swirling disk surrounding the black hole. Processes in the disk tap the tremendous gravitational energy of the black hole to propel material outward from the poles of the disk.

NGC 253, aka the Sculptor Galaxy, is also blowing out gas but as the result of star formation (Image: T.A. Rector/University of Alaska Anchorage, T. Abbott and NOAO/AURA/NSF)
NGC 253, aka the Sculptor Galaxy, is also blowing out gas but as the result of star formation (Image: T.A. Rector/University of Alaska Anchorage, T. Abbott and NOAO/AURA/NSF)

At the ends of both jets, the researchers found clumps of hydrogen gas moving outward from the galaxy at 1,000 kilometers per second. One of the clouds has much as 16,000 times the mass of the Sun, while the other contains 140,000 times the mass of the Sun.

The larger cloud, the scientists said, is roughly 160 by 190 light-years in size.

“This is the most definitive evidence yet for an interaction between the swift-moving jet of such a galaxy and a dense interstellar gas cloud,” Morganti said. “We believe we are seeing in action the process by which an active, central engine can remove gas — the raw material for star formation — from a young galaxy,” she added.

The researchers published their findings in the September 6 issue of the journal Science.

Source: NRAO press release

Our Galaxy’s Supermassive Black Hole is a Sloppy Eater

Like most galaxies, our Milky Way has a dark monster in its middle: an enormous black hole with the mass of 4 million Suns inexorably dragging in anything that comes near. But even at this scale, a supermassive black hole like Sgr A* doesn’t actually consume everything that it gets its gravitational claws on — thanks to the Chandra X-ray Observatory, we now know that our SMB is a sloppy eater and most of the material it pulls in gets spit right back out into space.

(Perhaps it should be called the Cookie Monster in the middle.*)

New Chandra images of supermassive black hole Sagittarius A*, located about 26,000 light-years from Earth, indicate that less than 1% of the gas initially within its gravitational grasp ever reaches the event horizon. Instead, much of the gas is ejected before it gets near the event horizon and has a chance to brighten in x-ray emissions.

The new findings are the result of one of the longest campaigns ever performed with Chandra, with observations made over 5 weeks’ time in 2012.

Read more: Chandra Stares Deep into the Heart of Sagittarius A*

“This new Chandra image is one of the coolest I’ve ever seen,” said study co-author Sera Markoff of the University of Amsterdam in the Netherlands. “We’re watching Sgr A* capture hot gas ejected by nearby stars, and funnel it in towards its event horizon.”

As it turns out, the wholesale ejection of gas is necessary for our resident supermassive black hole to capture any at all. It’s a physics trade-off.

“Most of the gas must be thrown out so that a small amount can reach the black hole”, said co-author Feng Yuan of Shanghai Astronomical Observatory in China. “Contrary to what some people think, black holes do not actually devour everything that’s pulled towards them. Sgr A* is apparently finding much of its food hard to swallow.”

X-ray image of Sgr A*
X-ray image of Sgr A*

If it seems odd that such a massive black hole would have problems slurping up gas, there are a couple of reasons for this.

One is pure Newtonian physics: to plunge over the event horizon, material captured — and subsequently accelerated — by a black hole must first lose heat and momentum. The ejection of the majority of matter allows this to occur.

The other is the nature of the environment in the black hole’s vicinity. The gas available to Sgr A* is very diffuse and super-hot, so it is hard for the black hole to capture and swallow it. Other more x-ray-bright black holes that power quasars and produce huge amounts of radiation have much cooler and denser gas reservoirs.

Illustration of gas cloud G2 approaching Sgr A* (ESO/MPE/M.Schartmann/J.Major)
Illustration of gas cloud G2 approaching Sgr A* (ESO/MPE/M.Schartmann/J.Major)

Located relatively nearby, Sgr A* offers scientists an unprecedented view of the feeding behaviors of such an exotic astronomical object. Currently a gas cloud several times the mass of Earth, first spotted in 2011, is moving closer and closer to Sgr A* and is expected to be ripped apart and partially consumed in the coming weeks. Astronomers are eagerly awaiting the results.

“Sgr A* is one of very few black holes close enough for us to actually witness this process,” said Q. Daniel Wang of the University of Massachusetts at Amherst, who led the study.

Watch Black Holes: Monsters of the Cosmos

Source: Chandra press release. Read the team’s paper here.

Image credits: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI


*Any resemblance of Sgr A* to an actual Muppet, real or fictitious, is purely coincidental.