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| PRI (MPIfR) 07/2009 (4) | Press Release | July 29, 2009 |
An international team of astronomers, led by Keiichi Ohnaka at the Max Planck Institute
for Radio Astronomy (MPIfR) in Bonn, has taken the sharpest view of a dying mammoth
star ever made. For the first time they could show, how the gas is moving in different areas
over the surface of a distant star. This was made possible by combining three 1.8 m
telescopes as an interferometer, giving the astronomers the resolving power of a
virtual, gigantic 48 m telescope.
Using the ESO VLT Interferometer in Chile, they discovered that the gas in the dying star’s atmosphere
is vigorously moving up and down, but the size of such “bubbles” is as large as the star itself.
These colossal bubbles are a key for pushing material out of the star’s atmosphere into space,
before the star explodes as a supernova. (Astronomy & Astrophysics, 2009, in press).
Figure 1:
Artist's impression, showing how a vast amount of material is flung out from
Betelgeuse into space. The supergiant's diameter exceeds the
dimensions of the inner solar system (the orbit of Mars would easily fit within the star).
The observations show, for the first time, how
gigantic bubbles are moving up and down over the star's surface.
A plume extending to a huge distance into space was found by another team of
astronomers
using a different VLT instrument (NACO).
Image: ESO/L. Calcada
(High resolution versions
with and
without scales, turned by 90 degrees).
When one looks up the clear night sky in winter, it is easy to spot a bright, orange star on the shoulder of the constellation Orion (the Hunter) even in light-flooded big cities. That is Betelgeuse. It is a mammoth star, which is so huge as to almost reach the orbit of Jupiter, swallowing the inner planets Mercury, Venus, Earth, and Mars, when placed at the center of the solar system. It is also glaringly bright, emitting 100 000 times more light than the Sun. Betelgeuse is a so-called red supergiant and approaching the end of its short life of several million years. Red supergiants shed a large amount of material made of various molecules and dust, which are recycled for the next generation of stars and planets possibly like the Earth. As a matter of fact, Betelgeuse is losing material equivalent to the Earth’s mass every year.
How these mammoth stars can lose mass, which would normally be bound to the star by the gravitational pull? This is a long-standing mystery. The best way to tackle this issue is to observe the scene where the material is ejected from a star’s surface, but this is a very challenging task. Although Betelgeuse is such a huge star, it looks like a mere reddish dot even with the today’s largest, 8–10 m telescopes, because the star is 640 light years away (the diameter of 1.3 billion km appears as 43 milli-arcseconds (mas) in that distance).
So, astronomers need a special technique to overcome this problem. By combining two or more telescopes as a so-called interferometer, astronomers can achieve a much higher resolution than provided with individual telescopes. The Very Large Telescope Interferometer (VLTI) on Cerro Paranal in Chile, operated by the European Southern Observatory (ESO), is one of the world’s largest interferometer. A team of astronomers in German, French, and Italian institutions observed Betelgeuse with the AMBER instrument operating at near-infrared wavelengths. The resolving power achieved with AMBER is so great that one can recognize a 1-Euro coin placed on the Brandenburg Gate in Berlin from Bonn.
“Our AMBER observations mark the sharpest view ever made on Betelgeuse”, says Keiichi Ohnaka at the MPIfR, the first author of the publication presenting the result. “And for the first time, we have spatially resolved the gas motion in the atmosphere of a star other than the Sun. Thus, we could observe how the gas is moving in different areas over the star’s surface.”
The AMBER observations have revealed that the gas in Betelgeuse’s atmosphere is moving vigorously up and down. The size of these “bubbles” is also gigantic, as large as the supergiant star itself (that is, one bubble as large as the orbit of Mars is moving at some 40 000 km/h). While the origin of these bubbles is not yet entirely clear, the AMBER observations have shed new light on the question about how red supergiant stars lose mass: such colossal bubbles can expel the material from the surface of the star to space. It also means that the material is not spilling out in a quiet, ordered way, but is flung out more violently in arcs or clumps.
The death of the mammoth star, which is expected in the next few thousand to
hundred thousand years, will
be accompanied by cosmic fireworks known as a supernova like the famous SN1987A. However, as
Betelgeuse is much closer to the Earth than SN1987A, the supernova can be
clearly seen with the unaided eye, even in daylight.
Figure 2:
Getting ready for the observations on Cerro Paranal. Two of the 1.8-m Auxiliary
Telescopes (ATs) have opened their domes. The third telescope is about to
be opened.
One of the domes of the 8.2 m UTs
is seen in the background.
Image: K. Ohnaka, MPIfR (taken with a film camera).
Click image for higher resolution.
Spatially resolving the inhomogeneous structure of the dynamical atmosphere of Betelgeuse with VLTI/AMBER
,
K. Ohnaka, K.-H. Hofmann, M. Benisty, A. Chelli, T. Driebe, F. Millour, R. Petrov, D. Schertl, Ph. Stee, F. Vakili, G. Weigelt,
Astronomy & Astrophysics, 2009, in press
(DOI: 10.1051/0004-6361/200912247).
Sharpest views of Betelgeuse reveal how supergiant stars lose mass, ESO Press Release 27/09, July 29, 2009.
Close-up of a dying heavyweight, MPIfR Press Release, May 27, 2008.
The Behemoth Has a Thick Belt,
ESO Press Release, May 27, 2008.
Max Planck Institute for Radio Astronomy (MPIfR)
Infrared Interferometry Group
at MPIfR.
European Southern Observatory (ESO).
VLT Interferometer (VLTI) of the
European Southern Observatory (ESO).
Astronomical Multi-BEam combineR (AMBER) at ESO/Paranal.
AMBER Homepage of the AMBER consortium.
The close circumstellar environment of Betelgeuse - Adaptive optics
spectro-imaging in the near-IR with VLT/NACO,
P. Kervella et al., 2009, Astronomy & Astrophysics (in press).
Dr. Keiichi Ohnaka,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-353
Fax: +49-228-525-229
E-mail: kohnaka (at)
mpifr.de
Prof. Dr. Gerd Weigelt,
Director, Infrared Interferometry Group,
Max-Planck-Institut für Radioastronomie, Bonn.
Fon: +49-228-525-243
Fax: +49-228-525-229
E-mail: weigelt (at)
mpifr.de
Dr. Norbert Junkes,
Public Outreach,
Max-Planck-Institut für Radioastronomie, Bonn.
Phone: +49-228-525-399
E-mail: njunkes (at)
mpifr.de
