Now that’s a wild ride!
Astronomers have discovered that the incredible gravitational
strength of supermassive black holes can tear planets away from their
star systems and hurl them through space at incredible speeds — as fast
as 30 million mph.
They noted that this is “a few percent” of the speed of light, a
theoretical constant of 186,000 miles per second or about 670 million
mph.
Called hypervelocity planets, the speedy worlds vastly outrace
runaway stars that scientists found flying out of our galaxy seven years
ago at the tortoise-like pace of just 1.5 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 astrophysicist
Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.
“You’d be in for a wild ride from the center of the
galaxy to the Universe at large.”
- Astrophysicist Avi Loeb
For this study, the researchers simulated a double-star system that
wanders too close to the supermassive black hole at the galactic center.
They had already known that the black hole’s gravitational forces could
rip the stars apart — sending one away at high speed while the other is
captured into orbit around the black hole.
But what would happen if each star had a planet or two orbiting
nearby?
The researchers 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 interstellar space 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.
“Other than subatomic particles, I don’t know of anything leaving our
galaxy as fast as these runaway planets,” added lead author Idan
Ginsburg of Dartmouth College.
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.
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