Runaway planets zoom at a fraction of light speed

Mar 22, 2012
In this artist's conception, a runaway planet zooms through interstellar space. New research suggests that the supermassive black hole at our galaxy's center can fling planets outward at relativistic speeds. Eventually, such worlds will escape the Milky Way and travel through the lonely intergalactic void. In this illustration, a glowing volcano on the planet's surface hints at active plate tectonics that may keep the planet warm. Credit: David A. Aguilar (CfA)

Seven years ago, astronomers boggled when they found the first runaway star flying out of our Galaxy at a speed of 1.5 million miles per hour. The discovery intrigued theorists, who wondered: If a star can get tossed outward at such an extreme velocity, could the same thing happen to planets?

New research shows that the answer is yes. Not only do runaway planets exist, but some of them zoom through space at a few percent of the speed of light - up to 30 million miles per hour.

"These warp-speed planets would be some of the fastest objects in our Galaxy. If you lived on one of them, you'd be in for a wild ride from the center of the galaxy to the Universe at large," said Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.

"Other than , I don't know of anything leaving our galaxy as fast as these runaway planets," added lead author Idan Ginsburg of Dartmouth College.

Such speedy worlds, called planets, are produced in the same way as hypervelocity . A double-star system wanders too close to the at the . Strong rip the stars from each other, sending one away at high speed while the other is captured into orbit around the black hole.

For this study, the researchers simulated what would happen if each star had a planet or two orbiting nearby. They found that the star ejected outward could carry its planets along for the ride. The second star, as it's captured by the black hole, could have its planets torn away and flung into the icy blackness of at tremendous speeds.

A typical hypervelocity planet would slingshot outward at 7 to 10 million miles per hour. However, a small fraction of them could gain much higher speeds under ideal conditions.

Current instruments can't detect a lone hypervelocity planet since they are dim, distant, and very rare. However, astronomers could spot a planet orbiting a hypervelocity star by watching for the star to dim slightly when the planet crosses its face in a transit.

For a hypervelocity star to carry a planet with it, that planet would have to be in a tight orbit. Therefore, the chances of seeing a transit would be relatively high, around 50 percent.

"With one-in-two odds of seeing a transit, if a hypervelocity star had a planet, it makes a lot of sense to watch for them," said Ginsburg.

Eventually, such worlds will escape the Milky Way and travel through the intergalactic void.

"Travel agencies advertising journeys on hypervelocity planets might appeal to particularly adventurous individuals," added Loeb.

Explore further: Telescopes hint at neutrino beacon at the heart of the Milky Way

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antialias_physorg
4.3 / 5 (12) Mar 22, 2012
Well, 1.5 million miles per hour is 0.2 percent of light speed. If you want to be pedantic about it then EVERY planet is "moving at a fraction of light speed".
dweeb
5 / 5 (1) Mar 22, 2012
look both ways when crossing the sidewalk
SteveL
3 / 5 (1) Mar 22, 2012
Well, 1.5 million miles per hour is 0.2 percent of light speed. If you want to be pedantic about it then EVERY planet is "moving at a fraction of light speed".

I had a simular thought, except that every >thing< moving is moving at a fraction of the speed of light. Silly title. Of course this means that we should also consider that difficult to spot extra-galactic objects could also be moving towards us at a fairly high rate of speed.
Scottingham
not rated yet Mar 22, 2012
they are effectively time machines into the future then, eh?
Deadbolt
1 / 5 (1) Mar 22, 2012
If they are moving that fast relatively towards and away from other stars, would it be easier for them to launch interstellar craft to stars in front of them?
Scottingham
5 / 5 (1) Mar 22, 2012
why not use the planet itself as an interstellar ship?
antialias_physorg
4.8 / 5 (6) Mar 22, 2012
why not use the planet itself as an interstellar ship?

Because planets are kinda hard to steer.

If they are moving that fast relatively towards and away from other stars, would it be easier for them to launch interstellar craft to stars in front of them?


Launch (as in "escape from the gravity of the planet"): No
give them a speed boost on the journey: Yes

But if 0.02% of light speed is considered a significant boost for your interstellar craft then you're in for a loooong trip, anyhow (and as soon as your target isn't dead center in front of your hypervelocity planet your speed boost will be less).

they are effectively time machines into the future then, eh?

Everywhere is. Just sit where you are. The future will come to you.
bhiestand
5 / 5 (1) Mar 23, 2012
The pedants are out in force today, and this time I entirely agree.
As a Trek fan, I'm shocked that any astrophysicist would misuse "warp-speed". Warp specifically refers to faster-than-light, and these planets don't come that close. Impulse drives can go much faster than this. Just saying ;)
kaypee
not rated yet Mar 23, 2012
If the motion was A LOT faster, blueshifted photons from the region of space in front of it might be sufficient to drive complex photochemistry, despite the lack of a nearby parent star.
antialias_physorg
not rated yet Mar 23, 2012
If the motion was A LOT faster, blueshifted photons from the region of space in front of it might be sufficient to drive complex photochemistry,

Hardly. Remember that these planets aren't attached to stars (and even then they wouldn't see any blueshift from their own star, since it's moving at roughly the same speed)

All these planets 'see' is a starry night. Not much photochemistry will be going on, there. These suckers are either very cold, or - if they are warm and have an atmosphere at all - the real power source is from internal heat (decay of radioisotopes)
kaypee
4 / 5 (1) Mar 23, 2012
antialias...heat is irrelevant. Heat does not cause photochemical reactions. Visible light photons that don't normally have enough energy to cause the electron transfers occuring in photochemistry may be able to do so if those photons are blueshifted.
panorama
not rated yet Mar 23, 2012
Bronson Beta?
antialias_physorg
not rated yet Mar 23, 2012
Heat does not cause photochemical reactions.

Why not? Heat (in the form of infrared radiation) is photons just as visible light is photons. The only difference is energy levels.

Point being: Even if the speed of the planet would cause a significant blueshift -the number of photons coming from, what is effectively a night sky, are so few that you won't find any fauna/flora being able to live off of that.
barakn
3 / 5 (2) Mar 23, 2012
Assuming an interstellar dust concentration of 10^7 particles per cubic meter, 10^5 atoms per particle, average atomic mass ~40 amu (calcium), one can calculate the power released by the constant bombardment of the particles at the center of the planet's leading face. For the extreme example of 30 million miles/hour, this works out to 800,000 watts per square meter, almost 600x more concentrated than sunlight. Under such conditions the surface is likely to be molten and the discussion of photochemistry is moot.
Au-Pu
1 / 5 (1) Mar 25, 2012
Barakn they are talking of 1.5 million miles per hour, not 30. Where is the relevance of your calculations to this?
BradynStanaway
5 / 5 (2) Mar 25, 2012
How about we start using the metric system FFS..
Graeme
5 / 5 (2) Mar 25, 2012
barakn you have a spectacular result, but I think your estimate of the number of particles is way off. Just plug the speed of earth into your formula and you could see that we would be all burning up at that rate.
Gigel
not rated yet Mar 26, 2012
Assuming an interstellar dust concentration of 10^7 particles per cubic meter, 10^5 atoms per particle, average atomic mass ~40 amu (calcium),

According to Wikipedia, the concentration would be something like 10^4 - 10^10 atoms / m3 (upper limit for some nebulae) and most atoms are H and He. Taking 1 amu,your computation would give an irradiance of 0.0002 - 200 W / m2. The upper limit is significant and corresponds to a surface temperature of 244 K or -29 degrees Celsius (compare to 15 deg. C average on Earth). Of course, there may be denser interstellar media. Such a planet may be detectable someday, misfortunatelly only during nebula passage; as it comes into more rarefied medium, it will stop heating.
barakn
1 / 5 (1) Apr 01, 2012
Barakn they are talking of 1.5 million miles per hour, not 30. Where is the relevance of your calculations to this?

I actually read the article, which stated that the first one was found at 1.5 million km/hr, 7-10 would be typical, and 30 million km/hr the upper limit. Did you read the article? Apparently not.
barakn
1 / 5 (1) Apr 01, 2012
Gigel, Graeme, point taken. I had a bad source for the dust concentration, must have been dust in the solar system ecliptic plane or something like that. This http://www.eso.or...uds2.ppt has an upper limit of 10^10 particles/m^3 (H2 mostly) for a molecular cloud, or about 2000x smaller than my number. Thus only 1/3 as strong as sunlight.
LariAnn
1 / 5 (1) Apr 17, 2012
Still, if a planet had been with a star long enough for life forms to evolve, once the planet went rogue, some truly bizarre forms of life might develop, given that the atmosphere and water is not lost and that there is a source of heat even without the star. Imagine a form of intelligent life on such a planet that has never seen sunlight from a star, only stars in the night sky!
antialias_physorg
not rated yet Apr 17, 2012
Imagine a form of intelligent life on such a planet that has never seen sunlight from a star, only stars in the night sky!

Last I checked the sun was also just a star in the sky.

And there are plenty nocturnal (or even cavebound/subterranean) species. Many nocturnal species look much like those that operate during the day with the sole exception of diffenernt primary senses (heat, ultrasonic, weak light sources, vibrations, smell, ... ) Why would you think that these creatures have to be 'truly bizarre'?

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