Astronomers have identified a brown dwarf — an object too large to be a planet but too small to be a star — with the ‘purest’ composition and the highest mass yet known.
An artist’s impression of the brown dwarf SDSS J0104+1535. Image credit: John Pinfield.
The brown dwarf in question is called SDSS J010448.46+153501.8 (J0104 for short).
This enigmatic object is located in the constellation of Pisces, approximately 750 light-years away from Earth.
It is a member of the halo of our Milky Way Galaxy, made up of the most ancient stars.
New observations by ESO’s Very Large Telescope (VLT) suggest that J0104 is made of gas that is around 250 times purer than the Sun, so consists of more than 99.99% hydrogen and helium.
It was previously not known if brown dwarfs could form from such primordial gas, and the discovery points the way to a larger undiscovered population of extremely pure brown dwarfs from our Galaxy’s ancient past.
“We really didn’t expect to see brown dwarfs that are this pure,” said Dr. Zeng Hua Zhang, an astronomer at the University of La Laguna and the Institute of Astrophysics in the Canary Islands.
“Having found one though often suggests a much larger hitherto undiscovered population — I’d be very surprised if there aren’t many more similar objects out there waiting to be found.”
Sloan Digital Sky Survey (SDSS) image of the field centered on SDSS J0104+15 (observation date October 13, 1999). The field is 2 arcmin on a side with north up and east to the left. Image credit: Z.H. Zhang et al.
Estimated to have formed about 10 billion years ago, VLT measurements also suggest J0104 — an L type subdwarf — has a mass equivalent to 90 times that of Jupiter, making it the most massive brown dwarf found to date.
Details of the research were recently published in the Monthly Notices of the Royal Astronomical Society. The article is also publicly available at arXiv.org.
_____
Z.H. Zhang et al. 2017. Primeval very low-mass stars and brown dwarfs – II. The most metal-poor substellar object. Mon Not R Astron Soc 468 (1): 261-271; doi: 10.1093/mnras/stx350
