Astronomers Discover Third-Closest Star System To Earth

The Bad Astronomer writes "Astronomers have found the third-closest star system to the Earth: called WISE 1049-5319, it's a binary brown dwarf system just 6.5 light years away. Brown dwarfs are faint, low mass objects 13 — 75 times the mass of Jupiter, and are so dim they are very difficult to detect. These newly-found nearby objects were seen in observations from 1978 but went unnoticed at the time, but since that date the large apparent motion of the binary made their proximity obvious. Only two star systems are closer: Alpha Centauri (4.3 light years) and Barnard's star (6 light years)."

Re:If brown dwarfs can't sustain fusion

[skade88]

According to the Brown Dwarf Wiki article "However, for some years now there has been debate concerning what criterion to use for defining the separation between a brown dwarf and a giant planet at very low brown dwarf masses (~13 Jupiter masses).[3] One school of thought is based on formation, and another on interior physics.[3] Dwarfs are categorized by spectral classification, with the major types being M, L, T, and Y.[3] Despite their name, most brown dwarfs would appear magenta to the human eye.[3] Another debate is whether brown dwarfs are required to have experienced fusion at some point in their history. Some planets are known to orbit brown dwarfs: 2M1207b, MOA-2007-BLG-192Lb, and 2MASS J044144b. Brown dwarfs may have fully convective surfaces and interiors, with no chemical differentiation by depth.[4]" http://en.wikipedia.org/wiki/Brown_dwarf [wikipedia.org]

Re:And where's the mass of the universe?

[Waffle Iron]

As I recall, it's because the orbital velocities of regular stars in disk-shaped galaxies suggest that dark matter is distributed spherically around the galactic center rather than concentrated in the disk. That implies that unlike brown dwarfs, dark matter interacts neither with normal matter nor itself by any force other than gravity.

Re:And where's the mass of the universe?

[Baloroth]

Can someone explain to me how discovering the THIRD closes system to ours in 2013 doesn't suggest that all the Dark Matter(tm) that's out there just isn't a mass of brown dwarfs that we can't see, and not a whole new class of matter?

Because of Big Bang nucleosynthesis. We can know how much baryonic matter ("normal" matter) there is in the universe by certain cosmological observations. Other cosmological observations show there is more matter out there than that (about 5 times more) and therefore it cannot all be brown dwarfs, black holes, or other dark but non-exotic forms of matter.

Re:And where's the mass of the universe?

[myrikhan]

IIRC there aren't enough of them and they're too low mass to make up the dark matter. After a bit of searching I found this thesis. It looks like a good introduction to the area.

http://arxiv.org/pdf/1110.2757 [arxiv.org]

Re:And where's the mass of the universe?

[Hentes]

The problem with that is if gravitational anomalies indeed are caused by a form of invisible matter, then its mass would have to be far too great to consist of normal matter. There are many forms of possibly invisible matter: compact stars, neutrinos etc but their masses don't add up [wikipedia.org] to even a fraction of the amount needed.

Re:Proxima Centauri

[PhotoJim]

True, but Proxima Centauri is a part of the Alpha Centauri star system, so that still makes this the third closest star system.

Re:And where's the mass of the universe?

[Waffle Iron]

No, it's the same gravity, which affects both normal matter and dark matter the same.

The difference is that if dark matter interacted by any force other than gravity (such as electromagnetism, etc.), then it would be deflected on encounters with other objects instead of passing right through them. This would eventually cause the dark matter to settle into a disk, like the rest of the stuff in the galaxy. However, it instead seems to remain in its initial spherical distribution to this day.