What the hell are these things?

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You know the drill, I find a paper detailing some wonderful discovery, waffle a bit of background and then give a glib summary of the conclusions. This is a bit different, this is the scientific process snow leopard caught outside it’s den, looking for a kill. Because the answer here is, “We don’t know”.

You might have heard of the Kepler telescope, it’s up there, looking for planets around other stars and maybe other things. It searches for planets by staring at a field with a lot of stars in it. If a planet orbiting one of the stars has an orbit with just the right alignment it can (once per orbit) get in the way of some of the light from the star, causing it to appear dimmer. Conversely, when the planet is on the other side of its orbit, the star can eclipse it, but given planets are much dimmer than stars, the effect on the measured brightness is small.

However, today this paper came out detailing two very strange discoveries. These are two objects, orbiting around two stars where the smaller object going behind the star causes a bigger dip in brightness than the smaller object passing in-front of the star. This means the smaller object must be pretty bright and as the authors calculate, pretty hot too. Using the data from the light curves of the star-object systems, they are able to calculate estimates for the size and temperature of these objects. One is between a fifth and a quarter of the Sun’s radius and about 9000°C, orbiting the parent star every 5 days. While the other is about a twelfth of the Sun’s radius, 10000°C and goes round its parent object every 23 days. To put these numbers into context, Jupiter is about a tenth of the Sun’s radius and a typical gas giant planet in the sort of orbits these objects are in would have temperatures below 2000°C.

So these objects are much, much hotter than they should be. So what are they? Well the authors speculate that they could be the hot remnants of stars stripped of their outer atmospheres. When stars age they puff up. If stars are in binary systems that are close enough, the binary companion can remove the outer layers of the star, leaving a small hot core. Perhaps this is one of these objects.

Strange, seemingly new classes of objects such as this will attract a lot of follow-up studies. The primary goal will be to work out what mass these objects are, the authors produce an estimates of the masses based on interactions between the objects, but an RV mass will be much more accurate. This will require measurements of the parent stars’ radial velocity.

So the conclusion of the paper, don’t know. Possibly the most interesting conclusion you can have in science.

Jason F. Rowe, William J. Borucki, David Koch, Steve B. Howell, Gibor Basri, Natalie Batalha, Timothy M. Brown, Douglas Caldwell, William D. Cochran, Edward Dunham, Andrea K. Dupree, Jonathan J. Fortney, Thomas N. Gautier III, Ronald L. Gilliland, Jon Jenkins, David W. Latham, Jack . J. Lissauer, Geoff Marcy, David G. Monet, Dimitar Sasselov, & William F. Welsh (2010). Observations of Transiting Hot Compact Objects Submitted to ApJL arXiv: 1001.3420v1

2 Comments on “What the hell are these things?”

  1. Niall says:

    There’s a paper now out with another mass estimate (still not RV) that agrees roughly with the results in the original paper. They’ve had a look at the potential evolution scenarios and they reckon these are the low mass white dwarfs, the remains of stars in binary systems that have had their outer layers stripped off by companions.

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