Andrew Yee
January 27th 06, 02:49 PM
Public Affairs Office
Harvard-Smithsonian Center for Astrophysics
For more information, contact:
David A. Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
Christine Pulliam, Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
For Immediate Release: Thursday, January 26, 2006
Release No.: 06-10
Two Exiled Stars Are Leaving Our Galaxy Forever
Cambridge, MA -- TV reality show contestants aren't the only ones under
threat of exile. Astronomers using the MMT Observatory in Arizona have
discovered two stars exiled from the Milky Way galaxy. Those stars are
racing out of the Galaxy at speeds of more than 1 million miles per hour
-- so fast that they will never return.
"These stars literally are castaways," said Smithsonian astronomer Warren
Brown (Harvard-Smithsonian Center for Astrophysics). "They have been
thrown out of their home galaxy and set adrift in an ocean of
intergalactic space."
Brown and his colleagues spotted the first stellar exile in 2005. European
groups identified two more, one of which may have originated in a
neighboring galaxy known as the Large Magellanic Cloud. The latest
discovery brings the total number of known exiles to five.
"These stars form a new class of astronomical objects -- exiled stars
leaving the Galaxy," said Brown.
Astronomers suspect that about 1,000 exile stars exist within the Galaxy.
By comparison, the Milky Way contains about 100,000,000,000 (100 billion)
stars, making the search for exiles much more difficult than finding the
proverbial "needle in a haystack." The Smithsonian team improved their
odds by preselecting stars with locations and characteristics typical of
known exiles. They sifted through dozens of candidates spread over an area
of sky almost 8000 times larger than the full moon to spot their quarry.
"Discovering these two new exiled stars was neither lucky nor random,"
said astronomer Margaret Geller (Smithsonian Astrophysical Observatory), a
co-author on the paper. "We made a targeted search for them. By
understanding their origin, we knew where to find them."
Theory predicts that the exiled stars were thrown from the galactic center
millions of years ago. Each star once was part of a binary star system.
When a binary swings too close to the black hole at the galaxy's center,
the intense gravity can yank the binary apart, capturing one star while
violently flinging the other outward at tremendous speed (hence their
technical designation of hypervelocity stars).
The two recently discovered exiles both are short-lived stars about four
times more massive than the Sun. Many similar stars exist within the
galactic center, supporting the theory of how exiles are created.
Moreover, detailed studies of the Milky Way's center previously found
stars orbiting the black hole on very elongated, elliptical orbits -- the
sort of orbits that would be expected for former companions of
hypervelocity stars.
"Computer models show that hypervelocity stars are naturally made near the
galactic center," said theorist Avi Loeb of the Harvard-Smithsonian Center
for Astrophysics. "We know that binaries exist. We know the galactic
center holds a supermassive black hole. So, exiled stars inevitably will
be produced when binaries pass too close to the black hole."
Astronomers estimate that a star is thrown from the galactic center every
100,000 years on average. Chances of seeing one at the moment of ejection
are slim. Therefore, the hunt must continue to find more examples of
stellar exiles in order to understand the extreme environment of the
galactic center and how those extremes lead to the formation of
hypervelocity stars.
The characteristics of exiled stars give clues to their origin. For
example, if a large cluster of stars spiraled into the Milky Way's central
black hole, many stars might be thrown out at nearly the same time. Every
known hypervelocity star left the galactic center at a different time,
therefore there is no evidence for a "burst" of exiles.
Hypervelocity stars also offer a unique probe of galactic structure.
"During their lifetime, these stars travel across most of the Galaxy,"
said Geller. "If we could measure their motions across the sky, we could
learn about the shape of the Milky Way and about the way the mysterious
dark matter is distributed."
The first newfound exile, in the direction of the constellation Ursa
Major, is designated SDSS J091301.0+305120. It is traveling out of the
galaxy at a speed of about 1.25 million miles per hour and currently is
located at a distance of about 240,000 light-years from the earth. The
second exile, in the direction of the constellation Cancer, is designated
SDSS J091759.5+672238. It is moving outward at 1.43 million miles per hour
and currently is located about 180,000 light-years from the earth.
Both stars, although traveling at tremendous speeds through space, are
located so far from the Earth that their motion cannot be detected except
with sophisticated astronomical instruments.
This research has been submitted to The Astrophysical Journal Letters for
publication and will be available online at
http://arxiv.org/abs/astro-ph/0601580
Authors on the paper are Brown, Geller, Scott Kenyon and Michael Kurtz
(Smithsonian Astrophysical Observatory).
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
Note to editors: Images to accompany this release are online at
http://www.cfa.harvard.edu/press/pr0610image.html
Harvard-Smithsonian Center for Astrophysics
For more information, contact:
David A. Aguilar, Director of Public Affairs
Harvard-Smithsonian Center for Astrophysics
617-495-7462
Christine Pulliam, Public Affairs Specialist
Harvard-Smithsonian Center for Astrophysics
Phone: 617-495-7463, Fax: 617-495-7016
For Immediate Release: Thursday, January 26, 2006
Release No.: 06-10
Two Exiled Stars Are Leaving Our Galaxy Forever
Cambridge, MA -- TV reality show contestants aren't the only ones under
threat of exile. Astronomers using the MMT Observatory in Arizona have
discovered two stars exiled from the Milky Way galaxy. Those stars are
racing out of the Galaxy at speeds of more than 1 million miles per hour
-- so fast that they will never return.
"These stars literally are castaways," said Smithsonian astronomer Warren
Brown (Harvard-Smithsonian Center for Astrophysics). "They have been
thrown out of their home galaxy and set adrift in an ocean of
intergalactic space."
Brown and his colleagues spotted the first stellar exile in 2005. European
groups identified two more, one of which may have originated in a
neighboring galaxy known as the Large Magellanic Cloud. The latest
discovery brings the total number of known exiles to five.
"These stars form a new class of astronomical objects -- exiled stars
leaving the Galaxy," said Brown.
Astronomers suspect that about 1,000 exile stars exist within the Galaxy.
By comparison, the Milky Way contains about 100,000,000,000 (100 billion)
stars, making the search for exiles much more difficult than finding the
proverbial "needle in a haystack." The Smithsonian team improved their
odds by preselecting stars with locations and characteristics typical of
known exiles. They sifted through dozens of candidates spread over an area
of sky almost 8000 times larger than the full moon to spot their quarry.
"Discovering these two new exiled stars was neither lucky nor random,"
said astronomer Margaret Geller (Smithsonian Astrophysical Observatory), a
co-author on the paper. "We made a targeted search for them. By
understanding their origin, we knew where to find them."
Theory predicts that the exiled stars were thrown from the galactic center
millions of years ago. Each star once was part of a binary star system.
When a binary swings too close to the black hole at the galaxy's center,
the intense gravity can yank the binary apart, capturing one star while
violently flinging the other outward at tremendous speed (hence their
technical designation of hypervelocity stars).
The two recently discovered exiles both are short-lived stars about four
times more massive than the Sun. Many similar stars exist within the
galactic center, supporting the theory of how exiles are created.
Moreover, detailed studies of the Milky Way's center previously found
stars orbiting the black hole on very elongated, elliptical orbits -- the
sort of orbits that would be expected for former companions of
hypervelocity stars.
"Computer models show that hypervelocity stars are naturally made near the
galactic center," said theorist Avi Loeb of the Harvard-Smithsonian Center
for Astrophysics. "We know that binaries exist. We know the galactic
center holds a supermassive black hole. So, exiled stars inevitably will
be produced when binaries pass too close to the black hole."
Astronomers estimate that a star is thrown from the galactic center every
100,000 years on average. Chances of seeing one at the moment of ejection
are slim. Therefore, the hunt must continue to find more examples of
stellar exiles in order to understand the extreme environment of the
galactic center and how those extremes lead to the formation of
hypervelocity stars.
The characteristics of exiled stars give clues to their origin. For
example, if a large cluster of stars spiraled into the Milky Way's central
black hole, many stars might be thrown out at nearly the same time. Every
known hypervelocity star left the galactic center at a different time,
therefore there is no evidence for a "burst" of exiles.
Hypervelocity stars also offer a unique probe of galactic structure.
"During their lifetime, these stars travel across most of the Galaxy,"
said Geller. "If we could measure their motions across the sky, we could
learn about the shape of the Milky Way and about the way the mysterious
dark matter is distributed."
The first newfound exile, in the direction of the constellation Ursa
Major, is designated SDSS J091301.0+305120. It is traveling out of the
galaxy at a speed of about 1.25 million miles per hour and currently is
located at a distance of about 240,000 light-years from the earth. The
second exile, in the direction of the constellation Cancer, is designated
SDSS J091759.5+672238. It is moving outward at 1.43 million miles per hour
and currently is located about 180,000 light-years from the earth.
Both stars, although traveling at tremendous speeds through space, are
located so far from the Earth that their motion cannot be detected except
with sophisticated astronomical instruments.
This research has been submitted to The Astrophysical Journal Letters for
publication and will be available online at
http://arxiv.org/abs/astro-ph/0601580
Authors on the paper are Brown, Geller, Scott Kenyon and Michael Kurtz
(Smithsonian Astrophysical Observatory).
Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.
Note to editors: Images to accompany this release are online at
http://www.cfa.harvard.edu/press/pr0610image.html