Exoplanet collision in BD+20 301. Possibly an Earth-like rocky exoplanet was involved? (Lynette Cook)

Hunt is on for “Killer” Third Star in BD+20 307 Binary System

10 Jan , 2009 by

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In September, it was announced the Chandra X-ray Observatory had spotted something very odd about BD+20 307. The binary system appeared to have a dusty disk surrounding it, indicative of a young, planet-forming system a fraction of the age of the Solar System. However, it was well known that the binary was actually several billion years old. It turns out that this disk was created by a rare planetary event; a cataclysmic planetary collision.

On Wednesday, at the AAS conference in Long Beach, I attended the “Extrasolar Planets” session to listen in on more results from Hubble about the exciting exoplanet discoveries in November… however, for me, the most captivating talk was about the strange, dusty old binary and the future detective work to be carried out to track down a planet killer…

The talks by astrophysicists working with the optical Hubble data were superb, showing off some of the science behind last years spate of direct observations of exoplanets, particularly the massive planet orbiting the star Fomalhaut, shaping a scattered disk of dust. However, there was no further news to report, apart from some cool numerical models the scientists will be using to characterize Fomalhaut b and a very interesting talk about the predicted lifetimes of exoplanets undergoing tidal stresses (which, unfortunately, I missed the first five minutes of as I got lost in the Long Beach Convention Center).

The one presentation that did pique my interest was Ben Zuckerman’s review of the progress being made in the study of BD+20 307. A few months ago, this piece of research caused a huge amount of interest as it provided the first piece of evidence of a huge, rocky planetary collision in the star system 300 light years away. Naturally, many news sources ran with article titles like: Is this what the Solar System would look like after Earth was hit by another planetary body? As Zuckerman pointed out, the fact that the group used an artist impression of a colliding Earth-like body (plus land masses and oceans, as pictured top) was no accident. BD+20 307 is certainly at an age when oceans might have formed and life–as Zuckerman morbidly conjectured–may have thrived. Not for any longer

Usually when we observe dust around a star, we can assume that it is a planet-forming star system that is fairly young. Conversely, as I found out to great depth in the conference, very old white dwarf systems can reveal a lot about their past planetary population when their dusty contaminants are studied. However, the dust contained in the BD+20 307 system is a puzzle. Astronomers had discovered a system, of comparable age to ours with a large amount of warm dust (T~500K). A system of that age will have long since expelled (via stellar wind pressure) or accreted any left-over dust from the planet-forming stages. Therefore, the only remaining explanation is that a rocky body collided with another, ejecting a huge amount of micron-sized warm dust particles.

So is this what the Solar System would look like after Earth is shattered by another planet? Possibly.

Zuckerman then pushed into some work being done to understand how the planetary collision could have happened in the first place. After all, the planets in our Solar System have settled into long-term stable orbits, any planet in BD+20 307 will have the same qualities. There were some questions as to whether the binary stars may have contributed to destabilizing the system, but Zuckerman quickly argued against this idea as the binary has such a tight orbit (with an orbital period of only 3.5 days), the destroyed planet will have found a stable orbit far from any gravitational variations.

So what could have caused the carnage in BD+20 307? We know that massive planetary bodies exert a huge gravitational pull on their host star and other planets in a system (i.e. Jupiter in the case of our Solar System), occasionally bullying (and sometimes capturing) them along the way. A small nudge in the wrong direction and planets could be knocked from their orbits, set on a collision course. So, much effort is now being put into a search for a third, faint star in BD+20 307. Perhaps it could be orbiting far away from the dancing binary, occasionally swinging past the planetary bodies, setting up the huge collision event.

This certainly seems reasonable, as 70% of binary star systems are found to have a third star. However, Zuckerman’s team have yet to find the “killer” third star and he appears confident that after careful analysis that there is no other stellar body within a 20 AU radius of the binary pair. Next, he intends to study the “wobble” of the centre of mass of the BD+20 307 binary to see if there is any gravitational anomaly as the mysterious “third star” tugs at the pair.


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Jon Hanford
Member
Jon Hanford
January 10, 2009 7:37 AM

Perhaps sentient life orbiting this star is just starting construction of its own Dyson sphere. On a more serious note, I wonder if spectra of the debris disk could shed any light on its progenitor and hence the approximate age and composition of planets in this system. Great story Ian, & good luck navigating the Long Beach Convention Center!

Kevin F.
Member
January 10, 2009 9:53 AM

On the picture, I’m sure that the weather systems on that planet would not be that pristine that far into a collision, nor would it still be that spherical.

Matthias
Guest
Matthias
January 10, 2009 12:14 PM

Well, if they are colliding (relatively) faster than the speed of sound within the plantes the collision can’t propagate ahead of the hit, so would basically stay intact (for fractions of a second).

Michael Paine
Guest
January 10, 2009 1:30 PM

Thanks for the report Ian
See my 2006 essay on the chances of observing the fireball from much smaller collisions of asteroids with extra-solar planets:
http://www.thespacereview.com/article/761/1

I am wondering if the conference that you attended considered this possibility?

Jorge
Guest
January 10, 2009 1:54 PM

Yeah, that’s my impression too…

… apart from the backlighting coming from nowhere and the impossible geometry of the suns and daysides, that is.

uncledan
Member
uncledan
January 10, 2009 5:18 PM

Hey! What else was said in the extrasolar planets presentation? I’ve been waiting for days for news in this area.

jason
Guest
jason
January 10, 2009 5:56 PM

Ease up on the nitpickery lol! Unlighted artwork would be less than helpful smile

DancesWithWords
Guest
January 10, 2009 6:56 PM

I’m surprised that a high density body passing near the system was not listed as a possibility? Or was it ruled out and not included in this post?

Gwydion
Guest
Gwydion
January 10, 2009 7:25 PM

It must be Nemesis! :OOO

Ray Finkle
Guest
Ray Finkle
January 11, 2009 4:12 AM

Oh noes, Nibiru draws nigh.

Joseph
Member
Joseph
January 11, 2009 7:08 AM

@ Ray: Lol

@ Ian And Kevin F: The artists depiction should be right, the two stars giving off light in the background are lighting up only a portion of the Earth-like planet, while most of it that we can see is shaded as if to be darkened. As well, isn’t it feasible that due to the impact and that there is basically molten lava exploding everywhere from the impact that it would slightly light up part of the planet that we can see?

Conic
Guest
January 11, 2009 7:34 AM

Boy my comments simply dont get posted anymore. That is a shame when people wind up saying things I had already said.

DancesWithWords
Guest
January 11, 2009 2:00 PM

Ian,

Maybe it is because I don’t understand the science or analysis of data, but I was thinking more along the lines of http://www.astronomycast.com/LIVE/nancy-atkinson/aas/invading-stars-faster-than-speeding-bullet/ neutron star or micro black hole. If one considers the age since the collision and factor in the distance one of these ultra high speed stellar objects is it not possible that are no longer in the area of data collection.

Feel free to poke hole in my suggestions.

Arik Rice
Guest
January 11, 2009 3:40 PM

“… apart from the backlighting coming from nowhere and the impossible geometry of the suns and daysides, that is.”

That’s from the flash of the camera, duh! smile

I also am amazed at the capabilities of said camera to capture both the surface features of the binary stars and the background stars. Contrast be damned!

Jorge
Guest
January 11, 2009 6:06 PM

LOL, Arik. That’s a good one! grin

RodBeaton
Member
January 12, 2009 5:00 PM

Interesting- A planetary collision of two planets in a binary star system.
How come the stars don’t collide?

Jupiter in our solar system gets into a ‘tug of
war’ with the sun every 12 years.
When that happens the ‘Earth’ gets pulled out
of its orbit for about two to three days, then it
returns.
I kind of doubt there is a third star, but ya
never know..
I think, instead there were two stable orbits
around the binary stars’ and they were just
naturally on a collision coarse- like the Earth,
billions of years ago, when a Mars size
object (might have) hit the earth creating our moon.

LLDIAZ
Guest
LLDIAZ
January 13, 2009 12:50 PM

Jupiter in our solar system gets into a ‘tug of
war’ with the sun every 12 years.
When that happens the ‘Earth’ gets pulled out
of its orbit for about two to three days, then it
returns.

Is this true and if it is what exactly pulls us back into orbit and what if we were’nt pulled back then what?

wpDiscuz