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First Image Of Planet-Like Body Orbiting A Star
deglr6328 writes "The Gemini North Telescope has, for the first time, directly imaged a planet like body orbiting a star. The object is a brown dwarf, 55 to 78 times the mass of planet Jupiter and 14 AU distant from its parent star 15 Sge. It was imaged using adaptive optics(see also here) that correct for the blurring effect of the atmosphere using deformable mirrors. Cool!"
while you're there
http://astra.hi.gemini.edu/gallery/science/
"Everyone is entitled to their own opinion, but not their own facts."
Like the article says, brown dwarves cannot be considered stars since they do not generate energy from a thermonuclear reaction. Having said that though, they DO give off more energy than they receive from outside sources, much like Jupiter does but on a far larger scale. A good primer site for brown dwarves can be found here .
Lastly, it is important to not confuse brown dwarves (almost stars) with white dwarves (dying stars).
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I didn't want to leave this space blank.
A brown dwarf is a star massive enough for deuterium fusion, but not massive enough for normal hydrogen to fuse.
What ever happene dto Gliese 229?
That was imaged back quite a while ago by a caltech team.
I found papers about it at Jean Schnieder's webpage, but not a listing...
Do you know why the road less traveled by is littered with the bones of the unwary?
I still have a high-school science book that states "a star will appear as a single point of light even in the largest telescopes"
Now we can see surface features on stars and even objects orbiting them. Pretty cool. Imagine what an orbiting interferometer will do!
Someone needs to mod the above up; it's important. I would have rephrased the post to reflect that this was NOT the first image of a brown dwarf orbiting a star if I knew about it before I submitted the comment.
On closer examination, the Gemini North press release does not claim to be the first to image a brown dwarf; from the site:"The faint companion is separated from its parent star by less than the distance between the Sun and the planet Uranus and is the smallest separation brown dwarf companion seen with direct imaging". It is only the CNN story that incorrectly claims this.....Hmmmm perhaps a notification is in order.
- "Hear that?! The percolations are imminent! Cease your ingress!"
As you can read, as far as 1995, the Hubble Space Telescope imaged a brown dwarf orbiting a brown dwarf on Gliese 229B. Indeed, some of the US media call it "the first discovered brown-dwarf" although the discoverer was Rafael Rebolo et al at the Instituto de Astrofísica de Canarias (he and his colleagues proposed the "Lithium test" method to actually detect this substellar objetcts). You can read a short report about brown dwarf findings at American Scientist.
Víctor R. Ruiz
rvr(at)blogalia.com
It's not a matter of whether or not Jupiter gets "lit". The sun was never "lit" as you speak of it. The sun is massive enough that the gravity well in the center is massive enough so that the nuclei of hydrogen particles collapse into helium (and these can collapse into heavier elements; our sun reaches it's limit around Oxygen. heavier elements are made in more massive stars). This collapse of nuclei into heavier nuclei is called fusion (gives off lotsa energy). Now for Jupiter to become a star it would have to be around the order of 100 times more massive than it is now (though that's still much less massive than the sun). With that much more mass it would definately affect the orbits (and possibly even the accretion, as there would have been an planet where the asteroid belt is were it not for Jupiter's current mass) of all the planets.
Also, the nuclear reactions going on inside the Earth and Jupiter's cores are fission based (decay of unstable elements). This is completely different from what's happening in the Sun so comparing this to what was happening in the early stages of the solar system is pointless.
As for the HST's future, it's scheduled for EOL at the end of the decade. Check out NASA's Next Generation Space Telescope page for its successor.
If Jupiter had somehow been lit ... it would have burned out in the deep, deep precambrian (billions of years ago). It doesn't have five billion years of fuel.
No. It would outlive the Sun. The larger a star is the greater the internal pressure, and the faster it burns fuel.
Small stars are long lived, large stars burn out fast.
- - You can't take something off the Internet! That's like trying to take pee out of a swimming pool.
The Law of Hydrostatic Equilibrium: Within every layer [of a star], the outward force of pressure equals the inward force of gravity.
Stars must have M 0.08 Msun to fuse hydrogen.
There exists a high-mass cutoff because very high mass stars cannot attain hydrostatic equilibrium. Very high mass stars produce enormous numbers of high-energy photons (L and T are both large). Photons exert pressure on gas (an effect called radiation pressure.) Ordinarily, the effects of radiation pressure are small, but for stars with M > 60 Msun, models indicate the radiation pressure is large enough to blow the star apart.
When a star exhausts the supply of H (hydrogen) in its core, it becomes a giant or supergiant, depending on its mass.
Once a star has used up all the H in its core, fusion of H into He (helium) stops. The core starts to contract just as it contracted as a protostar before H fusion began. As the core contracts, it releases energy. This energy heats up the layer immediately above the contracting He core. The layer immediately above the core becomes hot enough to initiate the fusion of hydrogen into helium.
The star now has three main layers:
(1) Helium core (inner layer): Releases energy as it shrinks in radius.
(2) Fusion shell: Releases energy as it fuses hydrogen into helium.
(3) Hydrogen envelope (outer layer): Absorbs energy, and swells greatly in size.
These swollen stars are now giants (if M 8 Msun).
Supergiants and giants with M > 0.4 Msun become hot enough to fuse He into C by the "triple alpha process", making primarily C (carbon), sometimes overshooting and making O (oxygen), and making Be (beryllium) as an intermediary product (and lots of gamma rays, too).
Once a giant or supergiant begins to fuse He in its core, it has four main layers.
Supergiants and giants with M > 3 Msun become hot enough to fuse C into heavier elements.
There is a limit to fusion: Iron (Fe).
The stages in the life of a 25 Msun star:
Hydrogen fusion lasts 7 million years
Helium fusion lasts 500,000 years
Carbon fusion lasts 600 years
Oxygen fusion lasts 6 months
Silicon fusion lasts 1 day
The star's core is now solid iron: end of the line as far as fusion is concerned.
Two choices:
(1) The star finds an alternative pressure source to maintain hydrostatic equilibrium which doesn't rely on the random thermal motions of atoms and ions; or
(2) The star collapses giving you:
a) black hole
or
b) nova/supernova
All clear now?
woof.
citations/references:8 starrfield.html
4 /n otes16.html
e r2 1.html
http://www.sciam.com/specialissues/0398cosmos/039
www-astronomy.mps.ohio-state.edu/~ryden/ast162_
cse.psc.sc.edu/hses/StarEvol/pages/reds.htm
blueox.uoregon.edu/~jimbrau/astr122/Notes/Chapt
www.imsa.edu/edu/astrophys/studentwork/inquiry/ (not as good)
An object below this limit is substellar, and may be either a Brown Dwarf or a planet. The distinction between both is somewhat fuzzy, and certainly to some degree arbitrary. One could argue that Brown Dwarfs and planets differ by their mode of formation - Brown Dwarfs form from collapsing gas clouds, like normal stars, while planets form from accretion of material in a circumstellar disk. However, establishing how a particular object has formed is not an easy task, so this is not a very practical definition.
Because Brown Dwarfs cool down over time, they eventually become cool enough for dust forming in their atmospheres, and they may show atmospheric phenomena (e.g. dust clouds) similar to those we know from planets. This is one of the reasons why surface imaging, either by direct imaging or with Doppler imaging, would be very interesting.
> The sun is massive enough that the gravity well
> in the center is massive enough so that the
> nuclei of hydrogen particles collapse into
> helium
The gravity of the sun isn't great enough to directly override the nuclear forces and cause fusion to occur. The weight of all the sun's material pressing inward because of that gravity, however, is great enough to cause fusion.
"All representatives are busy. The estimated hold time is one..hundred..sixty..four..minutes." Detroit Edison, 02/01/02
There are a few advantages that HST still has...
- AO works by measuring the distortions in the atmosphere and then compensating for them. But light from different parts of your field take slightly different paths through the atmosphere, and so are not perfectly corrected. As you get farther and farther away from the point where you measured the distortion, your corrections get worse and worse. The amount of sky that you can correct at once is quite small.
- In order to measure the distortions, you need a bright star that you can take as a point source. So bright that only about 1% of the sky is accessible. Artificial stars are still unreliable (but getting better).
- AO-corrected images have a really weird point spread function (PSF)... you have a fairly large halo of light around a sharp peak in the centre. Great for finding points, but hard for measuring how bright the entire thing is.
- The atmosphere blocks out a hell of a lot of the UV and IR light. No way of getting that back without going above the atmosphere.
So HST still has very unique capabilities. And just wait until we start seeing science out of the ACIS instrument!
[TMB]