Hyperfast star proven to be alien

Washington, D.C. - A young star is speeding away from
the Milky Way so fast that astronomers have been puzzled
by where it came from; based on its young age it has
traveled too far to have come from our galaxy. Now by
analyzing its velocity, light intensity, and for the first time
its tell-tale elemental composition, Carnegie astronomers
Alceste Bonanos and Mercedes Lopez-Morales, and
collaborators Ian Hunter and Robert Ryans from Queen's
University Belfast have determined that it came from our
neighboring galaxy, the Large Magellanic Cloud (LMC).

The result suggests that it was ejected from that galaxy
by a yet-to-be-observed massive black hole. The research
will be published in an upcoming issue of the Astrophysical
Journal Letters.

The star, dubbed HE 0437-5439, is an early-type star and
one of ten so-called hypervelocity stars so far found speeding
away from the Milky Way. "But this one is different from the
other nine," commented Lopez-Morales. "Their type, speed,
and age make them consistent with having been ejected
from the center of our galaxy, where we know there is a
super-massive black hole. This star, discovered in 2005,
initially appeared to have an elemental makeup like our
Sun's, suggesting that it, too, came from the center of our
galaxy. But that didn't make sense because it would have
taken 100 million years to get to its location, and HE 0437-5439
is only 35 million years old."

To explain the enigma, or "paradox of youth," the discoverers
proposed that HE 0437-5439 was either a so-called blue
straggler”a relatively young, massive star resulting from the
merger of two low-mass stars from the Milky Way, or it
originated from the Large Magellanic Cloud.

"We were intrigued by the conundrum and decided to take
up the challenge to solve this," stated Bonanos. "Stars in the
LMC are known to have lower elemental abundances than
most stars in our galaxy, so we could determine if its chemistry
was more like that galaxy's or our own."

The team confirmed results of the previous study concerning
the mass, age, and speed of the star. It is about nine times the
mass of our Sun, about 35 million years old, and it is zooming
away from the Milky Way and Large Magellanic Cloud into
intergalactic space at 1.6 million miles per hour (2.6 million
km/hour).

Although the previous study was able to roughly estimate
the star's elemental composition, the measurements were
not detailed enough to determine if the elements match
stars in our galaxy, or are characteristic of stars from the
Large Magellanic Cloud. These astronomers were able to
measure the relative abundances of certain elements for
the first time in any hypervelocity star. The relative
abundance of key elements tells them where a star
originated.

"We've ruled out that the star came from the Milky Way,"
explained Bonanos. "The concentration of elements in Large
Magellanic Cloud stars are about half those in our Sun.
Like evidence from a crime scene, the fingerprints point to
an origin in the Large Magellanic Cloud."

Based on the speed of the star's rotation measured by the
discoverers, and confirmed by this team, the astronomers
believe that the star was originally part of a binary system.
The binary could have passed close to a black hole 1,000
the mass of the Sun. As one star was pulled into the black
hole, the other was whipped into frenzy and flung out of
the galaxy.

"This is the first observational clue that a massive black
hole exists somewhere in the LMC. We look forward to finding
out where this black hole might be," concluded Bonanos.

http://www.ciw.edu/news/hyperfast_star_proven_be_alien