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Date: 23 Jul 2006 01:09:10
From: G S
Subject: Astronomers glimpse exploded star
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Astronomers glimpse exploded star
By Roland Pease
BBC Science
A star on the brink of exploding as a spectacular supernova has been
glimpsed by international astronomers.
The star flared up suddenly last February, briefly becoming 1,000
times brighter than normal.
RS Ophiuci is close to destroying itself in a nuclear explosion called
a type 1a supernova, scientists report in the journal Nature.
These are among the brightest phenomena in the Universe, radiating
five billion times as much light as the Sun.
They are so bright they can be seen far across the cosmos.
They also seem to be remarkably uniform - they always appear to give
off the same amount of light, so that their visibility from Earth,
dimmed only by their immense distance, has been used to measure the
size of the Universe.
The only problem, which is a great embarrassment to astronomers, is
that they have never seen a type 1a close up - their measurements are
all based on theory.
They are so rare that the last one known in our galaxy was seen in
1572 by the great Danish astronomer Tycho Brahe, who first coined the
term nova, for "new star", not realising he was in fact witnessing the
violent end of an unknown star.
Death throes
It has long been believed that type 1a supernovae are the death throes
of a white dwarf star. But all modern ones have been so distant that
it has not been possible to see what had been there beforehand.
RS Ophiuci, in the equatorial constellation of Ophiuchus (near Libra),
is just the right kind of white dwarf.
Several times in the past century it has flared up, as if in a failed
supernova explosion. It is as if a thermonuclear flame has swept
across the face of the star without quite catching hold.
The last time it flared up was in 1985, when astronomers' technology
was not up to catching all the details.
With space-based telescopes and large arrays of radio dishes, this has
all changed. Writing in the journal Nature, a team of astronomers said
they managed to detect a plume of gaseous material thrown out by the
conflagration.
"The explosion is so energetic it actually lifts an envelope of
material off the surface of the star and throws it off into space,"
lead author Jeno Sokoloski, of Harvard University, told the BBC's
Science in Action programme.
By tracking the plume, she adds, they could learn more about the star
that launched it.
"It started slowing down almost immediately, within just two days, and
that tells us the white dwarf must be extremely massive, in fact
almost massive enough to collapse."
Critical mass
Theory says that white dwarfs self destruct when their mass equals 1.4
Suns.
RS Oph is nearing that critical mass. It is slowly gobbling up
material from a nearby giant star, gaining a millionth of a solar mass
every decade.
At the moment, sitting just below the critical mass, the novae on RS
Oph blow themselves out, achieving brief episodes of brilliance.
But soon, RS Oph could pass the tipping point - the nuclear flame will
detonate from deep inside the star and blow it apart. How soon is not
clear.
"It could be tomorrow, but most likely it'll be 1,000, 10,000, 100,000
years from now," says Jeno Sokoloski.
Whenever it happens, it will be, she says, a spectacular event,
outshining the planets, so that its final glory will visible against
the day time sky.
In the meantime, astronomers will be studying the star closely, to
watch its every step towards destruction, and hoping to understand the
full details of one of the heaven's great mysteries.
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/5204676.stm
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Date: 23 Jul 2006 08:53:49
From: N:dlzc D:aol T:com \(dlzc\)
Subject: Re: Astronomers glimpse exploded star
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"G S" <GS@zaga.biz > wrote in message
news:6j46c21rmj1d435eqmqd47n36gpg9adtf6@4ax.com...
> RS Ophiuci is close to destroying itself in a nuclear explosion
> called
> a type 1a supernova, scientists report in the journal Nature.
http://antwrp.gsfc.nasa.gov/apod/ap060224.html
... about 3000 light years away. Flared in February too...
David A. Smith
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Date: 23 Jul 2006 14:19:51
From: jtaylor
Subject: Re: Astronomers glimpse exploded star
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"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@nospam.com > wrote in
message news:bYMwg.39095$AB3.16139@fed1read02...
>
> "G S" <GS@zaga.biz> wrote in message
> news:6j46c21rmj1d435eqmqd47n36gpg9adtf6@4ax.com...
> > RS Ophiuci is close to destroying itself in a nuclear explosion
> > called
> > a type 1a supernova, scientists report in the journal Nature.
>
> http://antwrp.gsfc.nasa.gov/apod/ap060224.html
> ... about 3000 light years away. Flared in February too...
>
This page:
http://www.aavso.org/vstar/vsots/0402.shtml
says RS Oph is a type 1B.
Nomenclature?
True disagreement?
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Date: 23 Jul 2006 10:32:51
From: Brian Tung
Subject: Re: Astronomers glimpse exploded star
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jtaylor wrote:
> http://www.aavso.org/vstar/vsots/0402.shtml
>
> says RS Oph is a type 1B.
>
> Nomenclature?
>
> True disagreement?
Based on the descriptions I've read for RS Ophiuchi, I'm guessing it's
a typo. I'm pretty sure a Type IB supernova is a massive star, not a
white dwarf accreting material from its companion.
--
Brian Tung <brian@isi.edu >
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.html
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Date: 23 Jul 2006 17:47:37
From: Sam Wormley
Subject: Re: Astronomers glimpse exploded star
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Brian Tung wrote:
> jtaylor wrote:
>
>>http://www.aavso.org/vstar/vsots/0402.shtml
>>
>>says RS Oph is a type 1B.
>>
>>Nomenclature?
>>
>>True disagreement?
>
>
> Based on the descriptions I've read for RS Ophiuchi, I'm guessing it's
> a typo. I'm pretty sure a Type IB supernova is a massive star, not a
> white dwarf accreting material from its companion.
>
Yes--From: http://en.wikipedia.org/wiki/Supernova#Type_Ib_and_Ic
Type Ib and Ic
The early spectra of Types Ib and Ic do not show lines of hydrogen nor
the strong silicon absorption feature near 615 nanometers. These events,
like supernovae of Type II, are probably massive stars running out of
fuel at their centers; however, the progenitors of Types Ib and Ic have
lost most of their envelopes due to strong stellar winds or interaction
with a companion. Type Ib supernovae are thought to be the result of a
Wolf-Rayet star collapsing. There is some evidence that Type Ic
supernovae may be the progenitors of gamma ray bursts, though it is also
thought that any core-collapse supernova (Type Ib, Ic, or II) could be a
GRB dependent upon the geometry of the explosion.
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Date: 24 Jul 2006 16:09:51
From: Dave
Subject: Re: Astronomers glimpse exploded star
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"They also seem to be remarkably uniform"
Not sure I understand, if they are so rare how do you know they are
remarkably uniform?
Dave
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Date: 24 Jul 2006 16:40:44
From: Chris L Peterson
Subject: Re: Astronomers glimpse exploded star
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On Mon, 24 Jul 2006 16:09:51 GMT, "Dave"
<Dave@pleasereplytonewsgroup.ca > wrote:
>"They also seem to be remarkably uniform"
>
>Not sure I understand, if they are so rare how do you know they are
>remarkably uniform?
It isn't that they are all that rare in the observable universe, just
rare in any given galaxy- in this case, ours. We see them regularly in
other galaxies, but it's been a few hundred years since the last one in
the Milky Way.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
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Date: 24 Jul 2006 13:14:40
From: robin_astro
Subject: Re: Astronomers glimpse exploded star
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G S wrote:
> Astronomers glimpse exploded star
> By Roland Pease
> BBC Science
>
>
> Story from BBC NEWS:
> http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/5204676.stm
Thanks for posting this update.
I took a series of spectra using simple equipment during this years
outburst
http://mysite.wanadoo-members.co.uk/astro2/spectra_24.htm
Perhaps the next one around 2025 might be a supernova!
Robin
www.leadbeaterhome.fsnet.co.uk/astro.htm
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