An Earthsized Telescope Observes Exploding Stars in Another Galaxy
7 December 1999
(Left) A MERLIN+VLA radio image of the central part of the nearby galaxy Messier 82 (M82) showing some of the supernova remnants present. Inset are images of the youngest remnant observed in 1986 and 1997, obtained by combining data from European radio telescopes which shows clear expansion over the 11 years. (Right) A highly detailed image, observed in November 1998, of the same remnant obtained from a 'World Array' of telescopes showing for the first time, the complex interaction of the ejected material with its surroundings.
British radio astronomers have used a telescope the size of the earth to peer into the heart of a nearby galaxy where they have found the scattered remains of stars that have torn themselves apart in catastrophic explosions. These remnants contain the heavy elements which are the building blocks for life itself and, for the first time, astronomers can now study in detail the mechanism by which this material is introduced and scattered into space. Their highly detailed images, from one of the largest radio astronomy experiments ever performed, will be presented at the December 10th meeting of the Royal Astronomical Society.
The astronomers are led by Dr. Alan Pedlar and Dr. Tom Muxlow of the Jodrell Bank Observatory (University of Manchester), and Dr. Karen Wills of Sheffield University. Using a collection of 20 radio telescopes spaced right around the earth, the team have produced an image of unprecedented detail of the galaxy known as M82. They found bright remnants of exploding stars and, comparing them with images taken many years ago, have found these shells of gas are expanding at up to 20,000 km every second. The youngest object they found to be only 35 years old.
The technique of combining the signals from radio telescopes spaced across continents results in very detailed pictures of the sky. The British astronomers have performed their observations with one of the largest ever collections of telescopes. It's as if they had a telescope 12,000 km across. Their maps of the sky are so detailed that they can see objects only 0.2 light years wide at the distance of M82 (10 million light years). The pictures are 30 times more detailed than can be obtained with the famous Hubble Space Telescope, and as Dr. Mike Garrett (another member of the observing team) from the Joint Institute for VLBI in Europe said. "This is equivalent to being able to read a newspaper in London from the Netherlands!"
The astronomer's target was the nearby starburst galaxy M82. Starburst galaxies, containing many billions of stars, are disturbed and are undergoing a rapid phase of star creation. Most new stars are quite small and live a long time like our local example, the Sun. But a small number of new stars are huge and evolve very rapidly - living for only a few million years or so. As Dr. Phil Diamond, director of the MERLIN/VLBI National Facility put it "These giant stars live fast and die young". So, paradoxically, the signature of such star-birth is the explosive death of massive stars.
When such large stars die, they do so in spectacular fashion. They blow themselves apart in a titanic explosion called a 'supernova'. The remnants of these supernovae are often expanding shell-like clouds of gas shining brightly in radio waves. Understanding such supernova remnants in regions where stars are being made is particularly important as it is thought that most galaxies, including our own, passed through this phase many billions of years ago when the Universe was young. However, the supernova remnants cannot easily be seen in visible light - even with the Hubble space telescope - because starburst galaxies contain a lot of obscuring dust. But, as Dr. Tom Muxlow explained, "Radio waves are unaffected by this dust and we are able to look right into the violent centre of the galaxy". The spectacular deaths of the massive stars in the centre of Messier 82, can be used to gain insights into the whole starburst phenomenon.
In this galaxy astronomers have seen, for the first time, the detailed evolution of the expanding fireball from a supernova explosion. And these distant and violent events have a strange twist in their tail. Dr. Karen Wills explained; "It is the death-throes of these massive stars which create the heavy elements from which life is made". All the material which makes up the Earth, the rocky planets and moons in our Solar System and indeed, our own bodies, was made in massive stars and scattered by such explosions in the early history of the Milky Way.
These latest results will be presented at the December 10th meeting of the Royal Astronomical Society by PhD student, and newest member of the team, Andy McDonald. This project also marks an important technical landmark in VLBI, in that this is the first time that the tape-recorded signals from 20 telescopes across the world have been simultaneously correlated. This was achieved by the the NRAO VLBA correlator facility in Socorro, New Mexico, USA.
The image (included in the html frame ) will be available as http://www.jb.man.ac.uk/news/primage1.gif
The team members below will be available at their host institutions on Wednesday 8th and Thursday 9th December. They will all be attending the Royal Astronomical Society Meeting on the Friday the 10th December at the Scientific Societies Lecture Theatre, Saville Row, London. The meeting starts at 10.30 am.
Dr Alan Pedlar, Jodrell Bank Observatory, University of Manchester.
Dr Tom Muxlow, MERLIN/VLBI National Facility, Jodrell Bank Observatory, University of Manchester.
Both on Phone: +44 (0)1477 571321
FAX: +44 (0)1477 571618
Alan Pedlar firstname.lastname@example.org
Tom Muxlow email@example.com
Dr Karen A. Wills, University of Sheffield.
Phone: +44 (0)114 222 4536
e-mail address K.Wills@sheffield.ac.uk
The 20 Radio Telescopes used to form the 'World Array' image are:
Lovell, UK EVN
Effelberg, Germany EVN
Medicina, Italy EVN
Noto Italy EVN
Onsala, Sweden EVN
Torun, Poland EVN
Westerbork, Netherlands EVN
From the US:
Kitt Peak VLBA
Los Alomos VLBA
Mauna Kea VLBA
North Liberty VLBA
Owens Valley VLBA
Pie Town VLBA
St Croix VLBA
From the Nasa Deep Space Network:
MERLIN (Multi Element Radio Linked Interferometer Network) is one of the most powerful radio telescopes in the world. It is operated by the University of Manchester on behalf of the Particle Physics and Astronomy Research Council (PPARC) and is the radio astronomy cornerstone of the United Kingdom's astronomy programme. MERLIN is a sensitive network of 7 telescopes distributed over central England, several at and near Jodrell Bank in Cheshire, one at Knockin near the Welsh border, one at Defford in Worcestershire and the newest located just outside Cambridge. MERLIN produces radio images with the same level of detail as that achieved optically with NASA's Hubble Space Telescope. More information can be found at http://www.jb.man.ac.uk/merlin.
The radio telescopes of MERLIN often participate in joint observations with similar telescopes in Europe and across the world. Using a technique known as Very Long Baseline Interferometry (VLBI) in which the signals from each telescope are recorded on large magnetic tapes and then replayed later on special purpose data processors, astronomers can synthesize a telescope with a diameter of up to 12,000 km. This allows them to produce radio images hundreds of times more detailed than the Hubble Space Telescope produces using visible light. More details on the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA) can be obtained from http://www.jive.nl/jive/evn/ and http://www.aoc.nrao.edu/pr/vlba.factsheet.html respectively.
The Very Large Array (VLA) is an array of 27 radio telescopes located in Socorro, New Mexico, USA. It is a powerful and highly versatile radio telescope operated by the National Radio Astronomy Observatory (NRAO) which is a facility of the National Science Foundation (NSF). The VLA does not have the high resolution capabilities of MERLIN but is much more sensitive to weak extended radio emission. When observing an object such as Messier 82 the combination of data from both telescopes is unbeatable and produces the superb image shown in the press release. More information on the VLA can be obtained from http://www.aoc.nrao.edu/vla/html/VLAintro.shtml.