by Charles Q. Choi
June 14, 2018
from Space Website



 

In the pair of colliding galaxies Arp 299, researchers spotted evidence of a supermassive black hole shredding a nearby star, pulling its debris into an orbiting disk and blasting a powerful jet of particles outward.

The background photo is a view of the colliding galaxies from the Hubble Space Telescope; an artist's concept of the black hole system is pulled out.
Credit: Sophia Dagnello/NRAO/AUI/NSF/NASA/STScI

A dust-enshrouded, giant black hole ripping apart a star blasted out a superfast jet of particles that packed about 125 billion times the amount of energy the sun releases per year, a new study finds.

This is the first time astronomers have directly imaged the formation and evolution of such a jet from a black hole. This finding may help astronomers discover many new instances of black holes destroying stars.

Supermassive black holes that are millions to billions times the mass of the sun are thought to lurk in the hearts of most, if not all, large galaxies.

If a star passes too close to such a monstrous black hole, its powerful gravitational pull will tear it apart in a so-called tidal disruption event.

As a black hole tears matter off a star, this material forms a rotating disk that glows brightly before it falls into the black hole.

Previous research also suggested that jets of particles are launched outward from the poles of these so-called accretion disks at extraordinarily high speeds.

Most times, supermassive black holes are not actively devouring anything, the new study's researchers told Space.com.

The small number of tidal disruption events that astronomers have detected so far offer scientists the chance to learn more about the formation and evolution of these jets.
 

Arp 299

Wikipedia

The first evidence that researchers had of this newly reported jet came on Jan. 30, 2005, from astronomers using the William Herschel Telescope in the Canary Islands to analyze a pair of colliding galaxies called Arp 299, nearly 150 million light-years from Earth.

They discovered a bright outburst of infrared light coming from the core of one of the colliding galaxies in Arp 299, study co-lead author Seppo Mattila, of the University of Turku in Finland, told Space.com.

On July 17, 2005, using the Very Long Baseline Array (VLBA) - a network of 10 radio telescopes spread across thousands of miles that can work together to essentially act like a giant radio telescope - scientists detected a new source of radio emissions from the same location in Arp 299.

"As time passed, the new object stayed bright at infrared and radio wavelengths, but not in visible light and X-rays," Mattila said in a statement.

 

"The most likely explanation is that thick interstellar gas and dust near the galaxy's center absorbed the X-rays and visible light, then re-radiated it as infrared," Mattila said.

This supermassive black hole shredding a star in the system Arp 299 resulted in an expanding, radio-emitting region, indicating a jet of particles moving outward.
Credit: Mattila, Perez-Torres, et al;

Bill Saxton/NRAO/AUI/NSF

The researchers initially thought this outburst was a star exploding in a supernova, but that explanation didn't match the data.

Continued monitoring over nearly a decade showed the source of radio emissions, dubbed Arp 299-B AT1, expanding in one direction, just as would be expected for a jet, but not for a supernova.

Radio data suggested the material in the jet raced outward at an average of about 25 percent the speed of light.

In contrast, the average expansion speed of a supernova after 10 years is expected to be, at most, about 5 percent of the speed of light, study co-lead author Miguel Pérez-Torres of the Astrophysical Institute of Andalusia in Granada, Spain, told Space.com.

"We continued to patiently collect more and more data to discern the true nature of this source, and our patience paid off," Mattila said.

 

"The combination of our infrared and radio observations, coupled with state-of-the art simulations of radio jets and calculations of infrared emission from the dusty regions surrounding a supermassive black hole, left us with one plausible explanation:

the infrared and the radio emission came from the disruption of a hapless star being devoured by the supermassive black hole when it passed too close to this cosmic monster."

The researchers estimated that this jet resulted from a supermassive black hole that was 20 million times the mass of the sun.

The black hole was situated at the core of one of the pair of colliding galaxies and it was in the act of shredding a star that was more than twice the sun's mass.

"Never before have we been able to directly observe the formation and evolution of a jet from one of these events," Pérez-Torres said in a statement.

The new findings were a surprise, the scientists said.

Arp 299-B AT1 was discovered as part of a project that sought to detect supernova explosions in colliding pairs of galaxies.

The transient Arp 299-B AT1

and its host galaxy Arp 299.

(A) A color-composite optical image from the Hubble Space Telescope (HST), with high resolution, 12.5 × 13 arcsecond size near-infrared 2.2 μm images [insets (B) and (C)] showing the brightening of the B1 nucleus (7).

 

(D) The evolution of the radio morphology as imaged with Very Long Baseline Interferometry (VLBI) at 8.4 GHz (7 × 7 milliarcsecond region centered at the 8.4 GHz peak position in 2005, RA = 11h28m30.9875529s, Dec = 58°33′40′′.783601 (J2000.0), indicated by the dotted lines).

 

The VLBI images are aligned with an astrometric precision better than 50 μas.

 

The initially unresolved radio source develops into a resolved jet structure a few years after the explosion, with the center of the radio emission moving westward with time (7).

 

The radio beam size for each epoch is indicated in the lower-right corner.

This infrared burst was originally thought to be a supernova explosion.

It was only in 2011, six years after the outburst's discovery, that Arp 299-B AT1 began to show the elongation that went on to reveal that it was a jet and not a supernova.

Over the course of about a decade, the jet released more than 1.5 x 10⁵² ergs of energy in infrared and radio waves, the researchers said. This is about 125 billion times the amount of energy the sun releases per year.

With the help of the VLBA, now the scientists are,

"witnessing how the radio source is now breaking up into several separate sources, telling us how the interaction of the jet with its surrounding medium is proceeding," Pérez-Torres said.

The event was not bright in visible or X-ray wavelengths, likely because of the effects of gas and dust, the scientists noted.

This may help explain why tidal disruption events are not as bright as theoretically predicted, they added.

"How many similar events are we missing in dusty centers of galaxies that would only be detectable by infrared and radio observations but be completely invisible in the optical light?" Mattila said.

These new findings suggest that infrared and radio telescopes may discover many tidal disruption events that may have escaped detection until now because dust absorbed any visible light from them, Pérez-Torres said.

Such events may have been more common in the early universe, so investigating them may help scientists understand the newborn cosmos, the researchers added.

The scientists detailed their findings (A Dust-enshrouded Tidal Disruption Event with a Resolved Radio Jet in a Galaxy Merger) online June 15 in the journal Science.