Size doesn't matter for

black holes
BY DR EMILY BALDWIN
ASTRONOMY NOW

Posted: September 22, 2008

Periodic X-ray signals are widely observed in low mass black holes, but now, for the first time, XMM-Newton has picked up similar signals from a supermassive black hole, confirming that black holes feed in the same way regardless of their size.

Artist impression of material falling into a supermassive black hole, forming an accretion disc and jets, together with the averaged shape of the periodic X-ray signal from REJ1034+396 as detected by XMM. Image: Aurore Simonnet, Sonoma State University (Adapted by M. Gierlinski).

When matter falls into a black hole it is heated up such that it emits X-rays at a certain frequency, which is detected as a periodic signal. The frequency of the signal is linked to the size of the black hole, with smaller objects emitting X-rays more frequently than larger ones. Most black holes observed in this way have masses on the order of ten solar masses. But scientists think that the same signals should also be emitted by supermassive black holes lodged at galactic centres, or active galactic nuclei (AGN), since the process of black hole accretion should be the same for all sizes. But these signals, until now, have not been observed in the largest known black holes.

“With more massive black holes where expected periods [of signal emission] are days or even months, the problem might be in the method the power spectrum is constructed, as it might decrease sensitivity to periodic signals,” says Dr Marek Gierlinski of the University of Durham, lead author of the paper in which the findings are reported. “So, it is easier to detect periodicity in a smaller supermassive black hole, and there are not too many of them.”

Using XMM, astronomers have found the rosetta stone of supermassive black holes, residing in a galaxy known only as RE J1034+396. The black hole itself is thought to be a million times as massive as our Sun, and emits a periodic signal once per hour. The finding confirms that even for an increase in black hole mass of a factor of one million, the same basic process for gas being sucked into a black hole remains the same. Now the quest is on to find out why some black holes show this behaviour and others don't, and to learn more about how matter behaves just before it falls into a black hole.

XMM has been in Earth orbit since 1999, and detects X-rays from objects that the Earth's atmosphere would otherwise block out. Image: ESA/ C. Carreau.

“Perhaps this particular object was unique, or we were very lucky,” says Gierlinski. “We don't know its mass well, but we suspect it is rather low for a supermassive black hole.”

The research group plan to continue their studies of REJ1034+396 for a much longer period, since the reported results are based on just 16 clear cycles of the pulsation.

“The long-term behaviour of the periodic signal, its phase and frequency variations would tell us a lot about these oscillations,” Gierlinski tells Astronomy Now. “This is something we cannot obtain from small black holes in binaries, as periods are very short. Secondly, REJ1034+396 has a rather special X-ray spectral shape, and we want to look at other similar objects.”

The results of the study are presented in the current edition of the journal Nature.

This special publication features the photography of British astro-imager Nik Szymanek and covers a range of photographic methods from basic to advanced. Beautiful pictures of the night sky can be obtained with a simple camera and tripod before tackling more difficult projects, such as guided astrophotography through the telescope and CCD imaging.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

Hubble Reborn
Hubble Reborn takes the reader on a journey through the Universe with spectacular full-colour pictures of galaxies, nebulae, planets and stars as seen through Hubble's eyes, along the way telling the dramatic story of the space telescope, including interviews with key scientists and astronauts.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

The Planets
From tiny Mercury to distant Neptune and Pluto, The Planets profiles each of the Solar System's members in depth, featuring the latest imagery from space missions. The tallest mountains, the deepest canyons, the strongest winds, raging atmospheric storms, terrain studded with craters and vast worlds of ice are just some of the sights you'll see on this 100-page tour of the planets.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

3D Universe
Witness the most awesome sights of the Universe as they were meant to be seen in this 100-page extravaganza of planets, galaxies and star-scapes, all in 3D!
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE

This new poster features some of the best pictures from NASA's amazing Mars Exploration Rovers Spirit and Opportunity.
 U.K. STORE
 E.U. STORE
 U.S. & WORLDWIDE STORE