Monday, June 6, 2016

Abundance of Objects Similar to WISE J0855-0714

Free-floating planetary-mass objects with masses around and below ~10 times the mass of Jupiter, and with temperatures below ~2200 K, are known to exist in star-forming regions and in clusters of stars younger than ~150 million years. These young planetary-mass objects are relatively luminous because they are cooling rapidly and are still in the process of contacting. This makes them much easier to detect than their older counterparts.

WISE J0855-0714 is currently the coldest known free-floating object beyond the Solar System. Using data from the Hubble Space Telescope (HST) and the Very Large Telescope (VLT), Osorio et al. (2016) show that the temperature of WISE J0855-0714 is somewhere between 225 to 250 K, consistent with previous observations. Additionally, WISE J0855-0714 has a low luminosity and a relatively high surface gravity. These properties indicate that WISE J0855-0714 is an old object.

WISE J0855-0714 is estimated to have 2 to 10 times the mass of Jupiter for an age of between 1 to 12 billion years. A lower mass would indicate a younger age since a lower-mass would allow WISE J0855-0714 to cool more rapidly to its current observed luminosity. If WISE J0855-0714 has a similar age as the Sun, its mass would be ~5 times the mass of Jupiter.

WISE J0855-0714 appears to represent an old version of similar mass objects that have been discovered in star-forming regions and in young clusters of stars. By extrapolating the known population of free-floating planetary-mass objects in young star clusters, it is estimated that there are around 15 to 60 objects like WISE J0855-0714 within ~20 light years of the Sun.

Osorio et al. (2016), "Near-infrared photometry of WISE J085510.74-071442.5", arXiv:1605.08620 [astro-ph.EP]