Integral catches a new erupting black hole

Nov 27, 2006
Integral catches a new erupting black hole
Artist's representation of an X-ray nova. The compact object on the right - a neutron star or a black hole – ‘swallows’ gas from a companion star. The gas swirls in a disk around the compact object at very high velocity (close to the speed of light) and emits X-rays. Credits: ESA

ESA's gamma-ray observatory, Integral, has spotted a rare kind of gamma-ray outburst. The vast explosion of energy allowed astronomers to pinpoint a possible black hole in our galaxy.

The outburst was discovered on 17 September 2006 by staff at the Integral Science Data Centre (ISDC), Versoix, Switzerland. Inside the ISDC, astronomers constantly monitor the data coming down from Integral because they know the sky at gamma-ray wavelengths can be a swiftly changing place.

"The galactic centre is one of the most exciting regions for gamma ray astronomy because there are so many potential gamma-ray sources," says Roland Walter, an astronomer at the ISDC, and lead author of these results.

To reflect the importance of this region, Integral is now running a Key Programme, in which almost four weeks of its observing time is given over to the study of the galactic centre. This is allowing astronomers to understand the gamma-ray characteristics of the galactic centre and its celestial objects, better than ever before.

Integral catches a new erupting black hole
This X-ray image was obtained by ESA's XMM-Newton satellite during the night of 22-23 September 2006, and shows the intense X-ray emission of the X-ray nova IGR J17497-2821. The X-ray nova was first spotted by ESA’s Integral gamma-ray observatory. Credits: ESA/EPIC/ISDC

It was during one of the first of these observations that astronomers saw the outburst take place. An unexpected event of this kind is known as a 'target of opportunity'. At first they did not know what kind of eruption they had detected. Some gamma ray outbursts last for only a short period of time and so they immediately alerted other observatories around the world of the outburst’s position, allowing them to target the explosion, too. Fortunately, Integral has the capability to pinpoint the position of such a very bright event incredibly accurately.

In this case, the outburst continued to rise in brightness for a few days before beginning a gradual decline that lasted for weeks. The way the brightness of an outburst rises and falls is known to astronomers as a light curve. "It was only after a week that we could see the shape of the light curve and realised what a rare event we had observed," says Walter.

Comparing the shape of the light curve to others on file revealed that this was an eruption thought to come from a binary star system in which one component is a star like our Sun whereas the other is a black hole.

In these systems, the gravity of the black hole is ripping the Sun-like star to pieces. As the doomed star orbits the black hole, it lays down its gas in a disc, know as an accretion disc, surrounding the black hole.

Occasionally, this accretion disc becomes unstable and collapses onto the black hole, causing the kind of outburst that Integral witnessed. Astronomers are still not sure why the accretion disc should collapse like this but one thing is certain: when it does collapse, it releases thousands of times the energy than at other times.

Because such active star–black hole binaries are thought to be rare in the Galaxy, astronomers expect Integral to see such an outbursts only once every few years. That makes each and every one a precious resource for astronomers to study.

Thanks to the quick reactions of the astronomers at ISDC, observations were taken with satellites and observatories all around the world. ESA's XMM-Newton X-ray observatory, NASA's Chandra and Swift space telescopes, numerous ground-based telescopes captured the elusive radiation from this cataclysmic event. Now astronomers are hard at work, understanding what it all means.

Source: European Space Agency

Explore further: Strange supernova is 'missing link' in gamma-ray burst connection

Related Stories

White dwarf may have shredded passing planet

Apr 17, 2015

The destruction of a planet may sound like the stuff of science fiction, but a team of astronomers has found evidence that this may have happened in an ancient cluster of stars at the edge of the Milky Way ...

Mystery of dwarf galaxy could be ejected black hole

Nov 19, 2014

An international team of researchers analyzing decades of observations from many facilities—including the W. M. Keck Observatory on Mauna Kea, the Pan-STARRS1 telescope on Haleakala and NASA's Swift satellite—has ...

Recommended for you

The riddle of galactic thin–thick disk solved

Apr 24, 2015

A long-standing puzzle regarding the nature of disk galaxies has finally been solved by a team of astronomers led by Ivan Minchev from the Leibniz Institute for Astrophysics Potsdam (AIP), using state-of-the-art ...

Giant cosmic tsunami wakes up comatose galaxies

Apr 24, 2015

Galaxies are often found in clusters, with many 'red and dead' neighbours that stopped forming stars in the distant past. Now an international team of astronomers, led by Andra Stroe of Leiden Observatory ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.