The Purple Rose of Virgo (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 17 Apr 2007 19:11:06 GMT
ESO Education and Public Relations Dept.
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Text with all links and the photos are available on the ESO Website at
URL:
http://www.eso.org/outreach/press-rel/pr-2007/pr-16-07.html
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For Immediate Release: 27 March 2007
ESO Press Photo 16/07
The Purple Rose of Virgo
VLT Image of Bright Supernova in Spiral Galaxy
Until now NGC 5584 was just one galaxy among many others, located to the
West of the Virgo Cluster. Known only as a number in galaxy surveys, its
sheer beauty is now revealed in all its glory in a new VLT image. Since 1
March, this purple cosmic rose also holds the brightest stellar explosion
of the year, known as SN 2007af.
Located about 75 million light years away towards the constellation Virgo
('the Virgin'), NGC 5584 is a galaxy slightly smaller than the Milky Way.
It belongs, however, to the same category: both are barred spirals.
Spiral galaxies are composed of a 'bulge' and a flat disc. The bulge hosts
old stars and usually a central supermassive black hole. Younger stars
reside in the disc, forming the characteristic spiral structures from
which the galaxies get their name. Barred spirals are crossed by a bright
band of stars. In 2000, using ESO's Very Large Telescope, astronomers
discovered the smallest, faintest, and most massive spirals.
In this amazing new image of NGC 5584 two dominant spiral arms are clearly
visible, while the others are deformed, probably due to interactions with
other galaxies. Luminous patches are spread all over the disc, indicating
that stars are being formed in this gigantic rose at a frantic pace.
Something even brighter, however, catches the eye in this picture. Any
image taken before the end of February would not have shown the luminous
spot located at the lower right of the galaxy's centre. As can be seen,
the newly found object is much brighter than the centre of the galaxy
itself. Its name? SN 2007af, the 32nd supernova discovered this year. Its
presence signals the dramatic death of a star with a mass comparable to
that of the Sun.
SN 2007af, the brightest supernova of the year (so far), was discovered on
1 March by the Japanese supernova hunter Koichi Itagaki. He pointed his
60-centimetre telescope towards the Virgo constellation and discovered
something that was not there before: SN 2007af. When it was discovered,
its brightness (apparent visible magnitude of 15.4) was about seven times
fainter than that of its host galaxy, NGC 5584. It has since brightened by
the same factor of 7, reaching an apparent magnitude of 13.3 and making it
observable by many amateur astronomers with smaller telescopes.
Observations on 4 March with ESO's New Technology Telescope at La Silla
revealed that this energetic explosion is a Type Ia supernova that was
observed a few days before it reached its maximal luminosity. Matter from
the doomed star is ejected with velocities above 15,000 km/s.
Astronomers are observing SN2007af with ESO's VLT, with the aim of
studying the geometry of the material ejected by the supernova, and
thereby better understanding the explosion mechanism (see also ESO 44/06).
A Type Ia supernova is thought to be the result of the explosion of a
small and dense star -- a white dwarf -- inside a binary system. As its
companion continuously spills matter onto the white dwarf, the white dwarf
reaches a critical mass, leading to a fatal instability and the supernova.
Type Ia supernovae are apparently quite similar to one another. This gives
them a very useful role as 'standard candles' that can be used to measure
cosmic distances. Their peak brightness rivals that of their parent
galaxy, hence qualifying them as prime cosmic yardsticks. Astronomers have
exploited this fortunate circumstance to study the expansion history of
our Universe.
However Type Ia supernovae are rare events: a galaxy like the Milky Way
may host a Type Ia supernova on average only every 400 years. Even so, SN
2007af is not the only brilliant detonation recently recorded in NGC 5584.
Furthermore, it seems that Japanese amateur astronomers have a special
talent for catching supernova explosions in this purple spiral. Indeed, in
1996 Aoki Masakatsu identified SN 1996aq in NGC 5584, a difficult to
classify supernova subject to a hot discussion due to its ambiguous
nature.
National contacts for the media:
Belgium: Dr. Rodrigo Alvarez, +32-2-474 70 50
Finland: Ms. Tiina Raivo, +358 9 7748 8369
Denmark: Dr. Michael Linden-Vørnle, +45-33-18 19 97
France: Dr. Daniel Kunth, +33-1-44 32 80 85
Germany: Dr. Jakob Staude, +49-6221-528229
Italy: Dr. Leopoldo Benacchio, +39-347-230 26 51
The Netherlands: Ms. Marieke Baan, +31-20-525 74 80
Portugal: Prof. Teresa Lago, +351-22-089 833
Sweden: Dr. Jesper Sollerman, +46-8-55 37 85 54
Switzerland: Dr. Martin Steinacher, +41-31-324 23 82
United Kingdom: Mr. Peter Barratt, +44-1793-44 20 25
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