The discovery of type Y brown dwarfs, the coldest of all the failed stars, has
finally been made official in two articles to be published in The Astrophysical
Journal Supplement Series. Brown dwarfs are bodies with dimensions intermediate
between those of planets and normal stars, not massive enough for nuclear fusion to
be triggered in their nucleus, and so are destined to simply cool slowly over time.
The discovery was made possible by the excellent sensitivity of the orbiting WISE
telescope to infrared light. WISE has found 100 brown dwarfs to date, and of these 6
have been confirmed as Y dwarfs, thanks to spectroscopic follow-up observations with
the most powerful ground-based telescopes, as well as the Hubble Space Telescope.
The coolest stars known up to now were the T dwarfs, with surface temperatures of a
few hundred degrees Celsius, the Y dwarfs can have surface temperatures as cold as a
few tens of degrees, with the record now held by WISE 1828+2650, at 25°C, colder than
the human body! (This object is the green point indicated by the arrow in the image
on the right, while on the left is an artist's impression of what the dwarf may look
like).
These objects are distinguished from giant planets only in that they are not in orbit
about a star but rather isolated in space, almost certainly created by accretion
within a protostellar cloud. Apart from this they shouldn't be too unlike giant
planets, so that their atmospheres may well look much like that of Jupiter.
In the
infrared these cold objects are about 5000 times brighter than in the optical light
that our eyes can detect, making detection with optical, ground-based telescopes
almost impossible.
The first 6 Y dwarfs recognised (the list will surely lengthen) have distances
between 9 and 40 light years, with the closest, WISE 1541-2250, actually becoming the
seventh closest star to Earth, even though some will argue that it isn't really a
star... |