# Hertzsprung-Russell Diagram gets new letter



## Metryq (Aug 24, 2011)

Just when you thought it was safe to punch your starship up to highway speeds between the stars...

*Discovered: Stars as Cool as the Human Body*

August 24, 2011: Scientists using data from NASA's Wide-field Infrared Survey Explorer (WISE) have discovered six "Y dwarfs"-- star-like bodies with temperatures as cool as the human body.

Astronomers hunted these dark orbs for more than a decade without success. When viewed with a visible-light telescope, they are nearly impossible to see. WISE's infrared vision allowed the telescope to finally spot the faint glow of a half dozen Y dwarfs relatively close to our sun, within a distance of about 40 light-years.

"WISE scanned the entire sky for these and other objects, and was able to spot their feeble light with its highly sensitive infrared vision," says Jon Morse, Astrophysics Division director at NASA Headquarters in Washington.

The Y's are the coldest members of the brown dwarf family. Brown dwarfs are sometimes referred to as "failed" stars. They are too low in mass to fuse atoms at their cores and thus don't burn with the fires that keep stars like our sun shining steadily for billions of years. Instead, these objects cool and fade with time, until what little light they do emit is at infrared wavelengths. The atmospheres of brown dwarfs are similar to those of gas giant planets like Jupiter, but they are easier to observe because they are alone in space, away from the blinding light of a parent star.

So far, WISE data have revealed 100 new brown dwarfs.  Of these, six are classified as cool Y's. One of the Y dwarfs, called WISE 1828+2650, is the record holder for the coldest brown dwarf with an estimated atmospheric temperature cooler than room temperature, or less than 80 degrees Fahrenheit (25 degrees Celsius).

"The brown dwarfs we were turning up before this discovery were more like the temperature of your oven," says Davy Kirkpatrick, a WISE science team member at the Infrared Processing and Analysis Center at Caltech. "With the discovery of Y dwarfs, we've moved out of the kitchen and into the cooler parts of the house."

The Y dwarfs are in our sun's neighborhood, from approximately nine to 40 light-years away. The Y dwarf approximately nine light-years away, WISE 1541-2250, may become the seventh closest star system, bumping Ross 154 back to eighth. By comparison, the star closest to our solar system, Proxima Centauri, is about four light-years away.

"Finding brown dwarfs near our sun is like discovering there's a hidden house on your block that you didn't know about," says Michael Cushing, a WISE team member at JPL. "It's thrilling to me to know we've got neighbors out there yet to be discovered. With WISE, we may even find a brown dwarf closer to us than our closest known star."

Once the WISE team identified brown dwarf candidates, they turned to NASA's Spitzer Space Telescope to narrow their list. To definitively confirm them, the WISE team used some of the most powerful telescopes and spectrometers on Earth to split apart the objects' light and look for telltale molecular signatures of water, methane and possibly ammonia. For the very coldest of the new Y dwarfs, the team used NASA's Hubble Space Telescope. The Y dwarfs were identified based on a change in these spectral features compared to other brown dwarfs, indicating they have a lower atmospheric temperature.


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## RJM Corbet (Aug 24, 2011)

If a few degrees difference in temperature is all they can find to write about them, brown dwarfs are still boringly aptly named ...


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## Vertigo (Aug 25, 2011)

Boring only until you slam into one in your starship because it was too cold for your sensors to spot it!


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## Nik (Aug 26, 2011)

"If a few degrees difference in temperature..."

Y would you say that ? These form another way-point on the gap between small stars and big planets...

Uh, we do seem to have two planet-building recipes, with the distinction being less which side of the 'snow line' their core formed, and more one core growing big enough to hang onto an atmosphere before the young star's solar wind zapped loose volatiles...

Then you've got sling-shot effects where close encounters between planetary cores may fling the smallest member out of the system. And, perhaps, these Y-types are the result of a minimal cloud collapse-- Literally, a 'Y' was all the birth-cloud had time to form before a nearby star's outburst swept the rest away. Remember those astonishing 'Pillars Of Creation' Hubble photos ?? Each 'fingertip' was a young solar system being robbed of volatiles...

Inward & outward migrations due to interactions with circum-solar disk just add to fun...


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## Metryq (Aug 27, 2011)

Or the fission idea has merit—as a stellar nebula collapses into a new system, the central mass fissions off blobs of mass that become planets. This would account for the conservation of angular momentum that the accretion theory does not.

I saw a recent article on rogue planets, starless, wandering through space. Either these are ejected by "slingshot" effects, or tossed out by fissioning. Perhaps the Y-dwarfs are out there with the rogue planets. If they are numerous enough, interstellar navigation may be much more dangerous than ever expected. That is, it might be comparatively safe close to a star where everything is cleared out and orderly.


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## RJM Corbet (Aug 27, 2011)

Give me pulsing neutron stars anytime, a teaspoon of which weighs as much as Z billion aircraft carriers and which can be used like lighthouses to navigate great galactic oceans ...


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## Metryq (Aug 27, 2011)

RJM Corbet said:


> Give me pulsing neutron stars anytime, a teaspoon of which weighs as much as Z billion aircraft carriers and which can be used like lighthouses to navigate great galactic oceans ...



Not very good for gardens...


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## RJM Corbet (Aug 27, 2011)

Metryq said:


> Not very good for gardens...



Yeah, that's also also cool: one zap and you're frizzed ...


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