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Researchers find that massive black holes halt star birth in distant galaxies

Modified image showing active black hole squashing star formation. Image: NASA/JPL-Caltech/R. Hurt

Massive black holes may exert control over the number of stars formed in the early lives of the galaxies in which they sit, astronomers working with the Herschel Space Observatory have shown in research published in the journal Nature today (10 May 2012).

Herschel data is helping to explain the link between the size of the central bulges of galaxies and the mass of their central black holes, say a team of astronomers led by Professor Seb Oliver from the University of Sussex.

All large galaxies have a massive black hole at their centre, each millions of times the mass of a single star. For over a decade scientists have been puzzled as to why the masses of the black holes are linked to the size of the round central bulges at the hearts of galaxies.

Galaxies with massive black holes were found to have high rates of star formation, with some forming stars at a thousand times the rate of our own Milky Way galaxy today.  But intriguingly, the Herschel results show that the fastest-growing black holes are in galaxies with very little star formation – once the radiation coming from close to the black hole exceeds a certain power, it tends to “switch off” star formation in its galaxy. 

Dr Mat Page of the Mullard Space Science Laboratory and lead author of the Nature paper says: “Space telescopes like Herschel let us look back in time, and that’s just what we need to do to find out how today’s galaxies were built. Galaxies were forming stars like crazy when the Universe was young, but trying to see the light from star formation against the glare from the hot stuff around the black hole has been almost impossible until now. That’s all changed with the new wavelengths opened up by Herschel’s SPIRE camera."

Professor Oliver co-leads the Herschel Multi-tiered Extragalactic Survey project (HerMES), responsible for mapping large regions of the sky and discovering hundreds of thousands of galaxies using images from the SPIRE camera onboard Herschel.

Observations were made of a small area of sky called the Chandra Deep Field North, which lies in the constellation of Ursa Major and has been observed by a number of observatories at a wide range of wavelengths. The Herschel data was taken as part of the HerMES project, which has recently issued its first data release (April 2012).

Professor Oliver says: “I am delighted that the HerMES team have been able make this breakthrough on such an important topic in astrophysics.  I am particularly proud of the people at Sussex who've been essential in making HerMES such a success.”

He adds: “This fantastic result provides an amazing link between black holes and star formation in the early Universe. It is a huge clue to this decade-old riddle and could mean that once a black hole is big enough and producing enough radiation, it somehow shuts down the formation of stars in the surrounding galaxy.

“The most likely explanation is that the incredibly strong winds from around these very powerful black holes are preventing the gas and dust in the rest of the galaxy from forming stars.” 

To study the early lives of galaxies, astronomers need to look at very distant galaxies, so far away that we see them as they were billions of years ago.

Although the black holes themselves cannot be seen, the material closest to them can get incredibly hot, emitting large amounts of light over a very wide range of wavelengths, from radio waves to x-rays.

The light from this super-heated material can be trillions of times as bright as the Sun, with brighter emissions indicating a more massive black hole. There are also strong flows of material (winds and jets) expelled from the region around the black hole.

The hot material near the black hole outshines almost all the light from rest of the host galaxy, except for the light with wavelengths just less than a millimetre.  This sub-millimetre light is invisible to normal telescopes but is seen by the Herschel Space Observatory and indicates the rate at which stars are being formed in the galaxy.

Notes for editors

'The suppression of star formation by powerful active galactic nuclei’, M. Page et al is published in the journal Nature, Thursday 10 May 2012.

Image caption and credit: Active Black Hole Squashes Star Formation NASA/JPL-Caltech/R. Hurt

HERSCHEL

The Herschel Space Observatory has shown that galaxies with the most powerful, active, supermassive black holes at their cores produce fewer stars than galaxies with less active black holes.

Supermassive black holes are believed to reside in the hearts of all large galaxies. When gas falls upon these monsters, the materials are accelerated and heated around the black hole, releasing great torrents of energy. In the process, active black holes oftentimes generate colossal jets that blast out twin streams of heated matter.

Inflows of gas into a galaxy also fuel the formation of new stars. In a new study of distant galaxies, Herschel helped show that star formation and black hole activity increase together, but only up to a point. Astronomers think that if an active black hole flares up too much, it starts spewing radiation that prevents raw material from coalescing into new stars.  

This artistically modified image of the local galaxy Arp 220, captured by the Hubble Space Telescope, helps illustrate the Herschel results. The bright core of the galaxy, paired with an overlaid artist's impression of jets emanating from it, indicate that the central black hole's activity is intensifying. As the active black hole continues to rev up, the rate of star formation will in turn be tamped down in the galaxy. Astronomers want to further study how star formation and black hole activity are intertwined.

HerMES

HerMES is the Herschel Multi-tiered Extragalactic Survey, an astronomical project to study the evolution of galaxies in the distant Universe. It is the largest project on ESA's Herschel Space Observatory.  The project is carried out by a large team, made up primarily of people who built one of the instruments on Herschel called SPIRE.  Hermes is also the Olympian messenger god, ruler of travelers, boundaries, weights and measures.

HerMES has mapped large regions of the sky using cameras that are sensitive to infrared radiation. We have discovered over 100 thousand galaxies. The light from most of these galaxies will have taken more than 10 billion years to reach us, which means we see them as they were 3 to 4 billion years after the big bang. Since the cameras are detecting infrared radiation they see star formation that is hidden from conventional telescopes. We expect that our cameras will catch many of the galaxies at the moment they are forming most of their stars. HerMES is led by Prof. Seb Oliver and Dr. Jamie Bock

UK Space Agency

The UK Space Agency is at the heart of UK efforts to explore and benefit from space.  It is responsible for all strategic decisions on the UK civil space programme and provides a clear, single voice for UK space ambitions.

Prof Seb Oliver: University of Sussex, Email: S.Oliver@sussex.ac.uk, Tel: +44 (0)1273 678852 +44(0)7971 019161

Madeleine Russell Press Officer, UK Space Agency Email: madeleine.russell@ukspaceagency.bis.gsi.gov.uk  Tel: +44 (0)1793 418069

University of Sussex Press office contacts: Maggie Clune and Jacqui Bealing. Tel: 01273 678 888. Email: press@sussex.ac.uk

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By: Maggie Clune
Last updated: Thursday, 10 May 2012

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