Monthly Archives: August 2016

Complex Brown Dwarf Systems ‘Baffle’ Astronomers

A couple of brown dwarfs have been discovered in a close binary system some 240 light years away, whose two stars circle each other at a distance of about 19AU, similar to that of Uranus around the Sun.   The two new exoplanets orbit close to the primary Sun-like star HD 87646 (1).  These two sub-stellar companions are HD 87646b, which is a minimum 12MJupiter sub-brown dwarf (a ‘hot Jupiter’-type exoplanet) orbiting every 13 days just 0.117AU from the star (2); and  HD 87646c, which is a 57MJupiter brown dwarf circling the star every 673 days (1).  The orbital eccentricity of the brown dwarf is greater than that of the inner sub-brown dwarf, which is in keeping with other observations of brown dwarfs orbiting stars.

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Image Credit: Janella Williams, Penn State University

The international team that discovered this remarkable system is perplexed as to how it might have come about:

“Given the fact that HD 87646 is the first known system to have two massive substellar objects orbiting a star in a close binary and the masses of the two objects are close to the minimum masses for burning deuterium and hydrogen, these peculiarities raise questions about the system’s formation and evolution.

“”The large masses of these two substellar objects suggest that they could be formed as stars with their binary hosts: a large molecular cloud collapsed and fragmented into four pieces; the larger two successfully became stars and formed the HD 87646 binary, and the other smaller ones failed to form stars and became the substellar objects in this system. This scenario might be relevant for the binary stars but seems problematic for the two substellar objects on orbits within one AU because it is unclear whether fragmentation on such a small scale can occur,” the paper reads (1)

“Other hypothesis offered by the scientists is that the two newly discovered giant objects were formed like giant planet in a protoplanetary disk around HD 87646A. However, they added that such massive disks are rare in close binaries, and further investigation is needed to confirm this explanation.” (3)

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On Proxima b

August 2016 saw the announcement of the discovery of an Earth-like planet orbiting our nearest neighbourhood star – the red dwarf Proxima Centauri.  The official press release was preceded by a leak to the German media from within the team of astronomers.  Here, I tell the story of the rumours of the announcement, and the wider implications of the discovery itself:

Rumours of an Earth-like Planet Orbiting Proxima Centauri

The German magazine Der Spiegel has reported that a major announcement is imminent:  there is an Earth-like planet orbiting the red dwarf star Proxima Centauri; the Sun’s closest stellar neighbour at 4.24 light years distance.

The magazine claims that the discovery was made by the European Southern Observatory (ESO) using the La Silla Observatory’s reflecting telescope in Chile, based upon a leak from an astrophysicist who has been working with the La Silla team (1).  This alleged discovery is in keeping with the current work being carried out at La Silla, as described in January earlier this year:

“What good news that the Pale Red Dot project is now planning a two-month observing campaign to search for potential Earth-analogs around Proxima Centauri using HARPS, the High Accuracy Radial velocity Planet Searcher spectrograph at the ESO La Silla 3.6m telescope. Nightly monitoring began on January 18th.” (2)

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Going the Wrong Way Round

A new Trans-Neptunian Object has been discovered whose quirkiness is breaking into new territory.  This object, currently named ‘Niku’ after the Chinese adjective for ‘rebellious’, is seriously off-piste and heading in a highly inclined, retrograde motion around the Sun (1).   Does this sound familiar?   The retrograde motion is something which Zecharia Sitchin claimed for the rogue planet Nibiru.  Niku…Nibiru.  It sounds like the team who discovered this object, based at the Harvard-Smithsonian Center for Astrophysics (2), are having a bit of fun with us.  Rest assured, this is not Nibiru, or anything like it.  That said, something in the past interacted with this object to fling it into its strange orbital path, and at the moment the identity of that strongly perturbing influence is a definitive ‘unknown‘.

Additionally, Niku’s discovery has prompted the astrophysics team to consider a new cluster of objects (high inclination TNOs and Centaurs) which appear to share the same orbital plane.  This, in itself, is an unexpected and exciting development.  Could the influencing factor be the mysterious Planet Nine (3)?

“…The new TNO appears to be part of another group orbiting in a highly inclined plane, so [Matthew] Holman’s team tested to see if their objects could also be attributed to the gravitational pull of Planet Nine.  It turns out Niku is too close to the solar system to be within the suggested world’s sphere of influence, so there must be another explanation. The team also tried to see if an undiscovered dwarf planet, perhaps similar to Pluto, could supply an explanation, but didn’t have any luck. “We don’t know the answer,” says Holman.” (1)

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