Black hole eats a super-Jupiter
Astronomers have watched as a black hole woke up from a decades-long
slumber to feed on a low-mass object – either a brown dwarf or a giant
planet – that strayed too close. A similar feeding event, albeit on a
gas cloud, will soon happen at the black hole at the centre of our own
Milky Way Galaxy.
The discovery in galaxy NGC 4845, 47 million light-years away, was made
by ESA’s Integral space observatory, with follow-up observations from
ESA’s XMM-Newton, NASA’s Swift and Japan’s MAXI X-ray monitor on the
International Space Station.
Astronomers were using Integral to study a different galaxy when they
noticed a bright X-ray flare coming from another location in the same
wide field-of-view. Using XMM-Newton, the origin was confirmed as NGC
4845, a galaxy never before detected at high energies.
Along with Swift and MAXI, the emission was traced from its maximum in
January 2011, when the galaxy brightened by a factor of a thousand, and
then as it subsided over the course of the year.
“The observation was completely unexpected, from a galaxy that has been
quiet for at least 20–30 years,” says Marek Nikolajuk of the University
of Bialystok, Poland, lead author of the paper in Astronomy & Astrophysics.
By analysing the characteristics of the flare, the astronomers could
determine that the emission came from a halo of material around the
galaxy’s central black hole as it tore apart and fed on an object of
14–30 Jupiter masses. This size range corresponds to brown dwarfs,
substellar objects that are not massive enough to fuse hydrogen in their
core and ignite as stars.
However, the authors note that it could have had an even lower mass,
just a few times that of Jupiter, placing it in the range of gas-giant
planets.
Recent studies have suggested that free-floating planetary-mass objects
of this kind may occur in large numbers in galaxies, ejected from their
parent solar systems by gravitational interactions.
The black hole in the centre of NGC 4845 is estimated to have a mass of
around 300 000 times that of our own Sun. It also likes to play with its
food: the way the emission brightened and decayed shows there was a
delay of 2–3 months between the object being disrupted and the heating
of the debris in the vicinity of the black hole.
“This is the first time where we have seen the disruption of a
substellar object by a black hole,” adds co-author Roland Walter of the
Observatory of Geneva, Switzerland.
“We estimate that only its external layers were eaten by the black hole,
amounting to about 10% of the object’s total mass, and that a denser
core has been left orbiting the black hole.”
The flaring event in NGC 4845 can be seen as a warm-up act for a similar
event expected in the supermassive black hole at the centre of our own
Milky Way Galaxy, perhaps even this year.
While there are no brown dwarfs or planets on the menu this time, a
compact cloud of gas amounting to just a few Earth masses has been seen
spiralling towards the black hole and is predicted to meet its fate
soon.
Along with the object seen being eaten by the black hole in NGC 4845,
these events will tell astronomers more about what happens to the demise
of different types of objects as they encounter black holes of varying
sizes.
“Estimates are that events like these may be detectable every few years
in galaxies around us, and if we spot them, Integral, along with other
high-energy space observatories, will be able to watch them play out
just as it did with NGC 4845,” says Christoph Winkler, ESA’s Integral
project scientist.
“Tidal disruption of a super-Jupiter in NGC 4845,” by M. Nikolajuk and R. Walter is published in Astronomy & Astrophysics, April 2013.
For further information, please contact:
Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer@esa.int
Marek Nikolajuk
University of Bialystok, Poland
Email: mrk@alpha.uwb.edu.pl
Roland Walter
University of Geneva, Switzerland
Email:
Roland.Walter@unige.ch
Christoph Winkler
ESA Integral Project Scientist
Email: cwinkler@rssd.esa.int
