Planets Hurtling near the Speed of Light? It's Possible, Study Says

Article excerpt

Scientists want to know if planets can form near the supermassive black hole at the core of the galaxy. If so, the black hole could fling them out into space at enormous speeds that, from our vantage point, could appear to approach the speed of light.

Deep in the heart of the Milky Way, where a supermassive black hole lurks, conditions are so chaotic that planets - and perhaps life - can't form: Or can they?

A small team of astronomers suggests one way to answer the question, at least as it relates to planets: Monitor the Milky Way's rejects - stars that the galaxy's central black hole has kicked toward intergalactic space - for signs of planets.

Such planets - orbiting a star or traveling alone - so far are hypothetical. The center of the galaxy is so shrouded in dust that planet-hunting as it's practiced in our galactic neighborhood is futile.

But individual ejected stars, dubbed hypervelocity stars because they are ejected at such great speeds, are anything but hypothetical. The first stellar speedster was reported to be leaving the galaxy in 2005. Since then, the total has grown to at least 16 hypervelocity stars reported.

Hunting for more in the galaxy's halo, where they are most obvious, then monitoring them for the signature of a planet's transit across the star's face, would help settle the question of whether the center of the galaxy is hospitable for planet formation, explains Avi Loeb, an astronomer at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

He is one of the co-authors of a paper set for publication in the Monthly Notices of the Royal Astronomical Society in Britain that looks at the ejection mechanism and how one might go about the hunt.

With planet-hunting efforts such as NASA's Kepler mission finding hundreds of confirmed planets, with at least 2,000 candidates waiting in the wings for confirmation, the notion that stars at the galactic center also host planets would seem reasonable.

But several factors could weigh against planet-making there, Dr. Loeb explains.

The broader region around the black hole is a hotbed of star formation. Stars are roughly a million times more densely packed there than the stars in the sun's neighborhood. At the galactic center, the stars that form generally are more massive than the sun, burn hotter, and flit about the galactic center at speeds of more than 2 million miles an hour, compared with roughly half a million miles an hour for the sun.

Under those cramped, turbulent conditions, it would be hard for a star's disk of dust and gas to hang together long enough to allow planets form.

Still some observations hint that planets might form close to the Milky Way's center.

For instance, researchers have noted intriguing flare-like events as material gets heated, compressed, then swallowed via the black hole's extraordinary gravitational tug. …


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