Y-type stars

July 11, 2017
An artist's conception of a brown dwarf star, an object that is more massive and hotter than a planet but not massive enough to become a normal star. Y-type brown dwarfs are the coolest subset with surface temperatures between about 200-500 degrees kelvin. A new study of the twenty-four known Y-dwarfs finds that the models for the coolest of them fail to explain the observed properties. Credit: NASA

Brown dwarf stars are failed stars. Their masses are so small, less than about eighty Jupiter-masses, that they lack the ability to heat up their interiors to the roughly ten million kelvin temperatures required for normal hydrogen burning (hydrogen burning fuels the Sun, whose surface temperature is about 5700 kelvin).

The and properties of depend on their precise masses and ages, and range from a few thousand degrees down to a mere 200 kelvin (comparable to the Earth's surface ) with the warmest group being designated as L Dwarfs, the next warmest group as T Dwarfs, and the coolest objects as Y Dwarfs. Not surprisingly, because they are so cool, brown dwarfs are faint and hard to detect, and so although theorists predict that there could be as many brown dwarf stars as there are normal stars our understanding of their evolution and interior properties is quite incomplete.

NASA's Wide-field Infrared Survey Explorer (WISE), which was sensitive to the emission from cool objects, discovered the Y class of brown dwarfs in 2011, and today there are twenty-four of them known.

CfA astronomer Caroline Morley and her colleagues used the Spitzer Space Telescope and the Gemini observatory, as well as some other facilities, to refine the distances, luminosities, colors, and spectral characteristics of these objects and compared the results to current models.

The scientists determined the masses and ages for twenty-two of them, and confirmed that, at least for the slightly warmer Y-dwarfs (whose temperatures are around 450 kelvin) the cloud-free surface models agree with observations.

All of them have elemental abundances comparable to those found in the Sun, and all appear to have turbulent atmospheres. However for the coolest few objects, whose temperatures are more like 250 kelvin, the models do not agree.

A larger sample of objects for study would help to constrain the parameters, but the authors note that it is unlikely more will be found until a more sensitive infrared mission is flown.

Explore further: Milky Way could be home to 100 billion 'failed stars'

More information: S. K. Leggett et al. The Y-type Brown Dwarfs: Estimates of Mass and Age from New Astrometry, Homogenized Photometry, and Near-infrared Spectroscopy, The Astrophysical Journal (2017). DOI: 10.3847/1538-4357/aa6fb5

Related Stories

Milky Way could be home to 100 billion 'failed stars'

July 5, 2017

Our galaxy could have 100 billion brown dwarfs or more, according to work by an international team of astronomers, led by Koraljka Muzic from the University of Lisbon and Aleks Scholz from the University of St Andrews. On ...

Brown dwarf companion stars

September 2, 2013

(Phys.org) —Astronomers trying to understand how the Sun and Earth formed, and why they have their characteristic properties, have made progress on a closely related problem: the nature of the lowest mass stars, so-called ...

Brown dwarfs hiding in plain sight in our solar neighborhood

September 6, 2016

Cool brown dwarfs are a hot topic in astronomy right now. Smaller than stars and bigger than giant planets, they hold promise for helping us understand both stellar evolution and planet formation. New work from a team including ...

Two new brown dwarf Solar neighbors discovered

July 15, 2011

Scientists from the Leibniz Institute for Astrophysics Potsdam (AIP) have discovered two new brown dwarfs at estimated distances of only 15 and 18 light years from the Sun. For comparison: The next star to the Sun, Proxima, ...

Astronomers discover coolest objects outside solar system

January 26, 2011

UK's University of Hertfordshire astronomers have measured the distances to 11 of the coolest objects ever discovered outside our solar system. The 11 cool objects – known as brown dwarfs – have masses intermediate ...

Recommended for you

No alien 'signals' from cigar-shaped asteroid: researchers

December 14, 2017

No alien signals have been detected from an interstellar, cigar-shaped space rock discovered travelling through our Solar System in October, researchers listening for evidence of extraterrestrial technology said Thursday.

Dawn of a galactic collision

December 14, 2017

A riot of colour and light dances through this peculiarly shaped galaxy, NGC 5256. Its smoke-like plumes are flung out in all directions and the bright core illuminates the chaotic regions of gas and dust swirling through ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

tblakely1357
not rated yet Jul 11, 2017
I wonder if a moon orbiting one of the warmer brown dwarfs could be habitable for Terran type life and for how long.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.