Press Release Mt. Stromlo & Siding Spring Observatories. (embargoed until: 10:00 am Monday 3 August 1997)
.	(last Modified: 31 July 1997)

Feeding the Monster: Gas Caught in its Death Spiral into a Massive Black Hole

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An international team of Astronomers led by Mt. Stromlo Professor Mike Dopita have used the Hubble Space Telescope to discover how a massive Black Hole in a nearby galaxy feeds itself.

The Black Hole is located at the centre of the Giant Elliptical galaxy M87 at the heart of the Virgo cluster of galaxies. Earlier Hubble Telescope data obtained by another team member, Professor Holland Ford of Johns Hopkins University in Baltimore, Maryland, had found a disk of gas rushing around the Black Hole at a speed of 500 kilometers a second. This shows that the Black Hole weighs in at nearly 3 billion times the mass of the sun.

The latest Space Telescope study used an image 100 times clearer than could be obtained from the earth together with a spectrum at Ultraviolet wavelengths that cannot penetrate the earth's atmosphere. Dopita's team have discovered that the disk is being fed by gas streams that shock against each other and so trap themselves into a death spiral which leads down into the Black Hole.

Explained Mark Allen, who is completing his PhD on Active Galaxies at Mt. Stromlo supervised by Professor Dopita; "thanks to the modelling code developed by Ralph Sutherland at the ANU Astrophysical Theory Centre, and by Mike Dopita at Mt Stromlo, we realised that if we obtained a spectrum covering both the ultraviolet and optical wavelengths, we could discover if shocks were important in feeding the monster. With the Space Telecope, we discovered shocks of 260 kilometers per second, which serve to squash the gas and to help it to feed down into the Black Hole".

The gas streams in M87 have come from millions of dying stars similar to our sun which have lost their outer layers. Some of this material wanders into the fierce gravity field of the Black Hole, and is trapped at the rate of nearly ten solar masses a year. However, a tiny fraction, about 0.2% of the total, manages to escape in the last minutes before it is dragged into the Black hole, and is instead squirted out in a jet which is bright in both the radio and the optical bands. Dr. Geoff Bicknell (also of Mt Stromlo) in a paper published last year proved that this jet of gas is flying out at nearly the speed of light and is carrying prodigious amounts of energy, equivalent to the light of 25 billion suns.

Mike Dopita points out that such research is only possible thanks to a Major Grant of the International Science and Technology Division of the Department of Industry, Science and Tourism. "Without this grant", he says, "it would be impossible to sustain Australian leadership of such international teams, and it would be much harder to win an Australian share of observation time on the Hubble Space Telescope in the face of the tremendous world-wide competition."

These results are due to be published in the Astrophysical Journal in December.

 

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About the Image:

• This jpeg -format image can be obtained electronically here:

   

• This tiff -format image can be obtained electronically here:

   

   

  

  A six orbit integrated image taken with the Hubble Space Telescope. This is taken in the light of hot, ionised hydrogen and clearly shows the inner gas disk caught in its death spiral into the Black Hole. The scale of the image in arc seconds is marked. The image covers a region that would take light 800 years to cross.

   

   

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  About the Team:

  The Australian team members are all based at the Australian National University. Mt. Stromlo & Siding Spring Observatories (MSSSO) is part of The Institute of Advanced Studies. The ANU Astrophysical Theory Centre is operated jointly by MSSSO and the School of Mathematical Studies (SMS).

  Professor Mike Dopita is based at Mt. Stromlo Observatory, and his home page is here:

  

  His interests are in the physics of the interstellar medium, planetary nebulae, supernovae and active galactic nuclei. He is a Fellow of the Australian Academy of Science.

  Dr. Geoff Bicknell is at the ANU Astrophysical Theory Centre and Mt. Stromlo, and his expertise is in high energy astrophysics, relativistic gas dynamics and the physics of jets in active galaxies.

  Dr. Ralph Sutherland is at the ANU Astrophysical Theory Centre and Mt. Stromlo, and his home page is here:

  

  Mark Allen is completing his PhD on Seyfert Galaxies, and his home page is at:

  

  The US team members are Prof. Holland Ford and Dr. Zlatan Tsvetanov both of John Hopkins University in Baltimore, and Dr. Anuradha Koratkar of the Space Telescope Science Institute. All specialise in the physics of active galaxies. Professor Ford was the first to identify the gas stream and estimate the mass of the Black Hole and his home page is here:

  

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Access no. 10929