Andrew Yee[_1_]
January 29th 08, 07:36 PM
Carnegie Institution of Washington
Contact:
Alcestes Bonanos, 202-478-8859
Monday, January 28, 2008
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.
* The astronomers who discovered HE 0437-5439 are Heinz Edelmann, Ralf
Napiwotzki, Uli Heber, Norbert Christlieb, and Dieter Reimers. The work was
published in Astrophys.J. 634, L191-L184, 2005.
** The work predicting that a 1,000 solar mass black hole is necessary to
eject the star can be found in Alessia Gualandris and Simon Portegies Zwart,
Mon.Not.Roy.Astron.Soc.Lett. 376 (2007) L29-L33.
Alceste Bonanos acknowledges research and travel support from the Carnegie
Institution of Washington through a Vera Rubin Fellowship. Mercedes
Lopez-Morales acknowledges support provided by NASA through Hubble
Fellowship grant HF-01210.01-A awarded by the Space Telescope Science
Institute, which is operated by the Association of Universities for Research
in Astronomy, Inc., for NASA, under contract NAS5-26555.
The Carnegie Institution (www.CIW.edu) has been a pioneering force in basic
scientific research since 1902. It is a private, nonprofit organization with
six research departments throughout the U.S. Carnegie scientists are leaders
in plant biology, developmental biology, astronomy, materials science,
global ecology, and Earth and planetary science.
Contact:
Alcestes Bonanos, 202-478-8859
Monday, January 28, 2008
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.
* The astronomers who discovered HE 0437-5439 are Heinz Edelmann, Ralf
Napiwotzki, Uli Heber, Norbert Christlieb, and Dieter Reimers. The work was
published in Astrophys.J. 634, L191-L184, 2005.
** The work predicting that a 1,000 solar mass black hole is necessary to
eject the star can be found in Alessia Gualandris and Simon Portegies Zwart,
Mon.Not.Roy.Astron.Soc.Lett. 376 (2007) L29-L33.
Alceste Bonanos acknowledges research and travel support from the Carnegie
Institution of Washington through a Vera Rubin Fellowship. Mercedes
Lopez-Morales acknowledges support provided by NASA through Hubble
Fellowship grant HF-01210.01-A awarded by the Space Telescope Science
Institute, which is operated by the Association of Universities for Research
in Astronomy, Inc., for NASA, under contract NAS5-26555.
The Carnegie Institution (www.CIW.edu) has been a pioneering force in basic
scientific research since 1902. It is a private, nonprofit organization with
six research departments throughout the U.S. Carnegie scientists are leaders
in plant biology, developmental biology, astronomy, materials science,
global ecology, and Earth and planetary science.