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British royal families fought the War of the Roses in the 1400s for
control of England's throne, a grouping of stars was waging its own
contentious skirmish — a star wars far away in the Orion Nebula.
The stars were battling each other in a gravitational tussle, which
ended with the system breaking apart and at least three stars being
ejected in different directions. The speedy, wayward stars went
unnoticed for hundreds of years until, over the past few decades, two of
them were spotted in infrared and radio observations, which could
penetrate the thick dust in the Orion Nebula.
The observations showed that the two stars were traveling at high
speeds in opposite directions from each other. The stars' origin,
however, was a mystery. Astronomers traced both stars back 540 years to
the same location and suggested they were part of a now-defunct
multiple-star system. But the duo's combined energy, which is propelling
them outward, didn't add up. The researchers reasoned there must be at
least one other culprit that robbed energy from the stellar toss-up.
Now NASA's Hubble Space Telescope has helped astronomers find the
final piece of the puzzle by nabbing a third runaway star. The
astronomers followed the path of the newly found star back to the same
location where the two previously known stars were located 540 years
ago. The trio reside in a small region of young stars called the
Kleinmann-Low Nebula, near the center of the vast Orion Nebula complex,
located 1,300 light-years away.
"The new Hubble observations provide very strong evidence that the
three stars were ejected from a multiple-star system," said lead
researcher Kevin Luhman of Penn State University in University Park,
Pennsylvania. "Astronomers had previously found a few other examples of
fast-moving stars that trace back to multiple-star systems, and
therefore were likely ejected. But these three stars are the youngest
examples of such ejected stars. They're probably only a few hundred
thousand years old. In fact, based on infrared images, the stars are
still young enough to have disks of material leftover from their
xtremely fast on their way out of the
Kleinmann-Low Nebula, up to almost 30 times the speed of most of the
nebula's stellar inhabitants. Based on computer simulations, astronomers
predicted that these gravitational tugs-of-war should occur in young
clusters, where newborn stars are crowded together. "But we haven't
observed many examples, especially in very young clusters," Luhman said.
"The Orion Nebula could be surrounded by additional fledging stars that
were ejected from it in the past and are now streaming away into
The team's results will appear in the March 20, 2017 issue of The Astrophysical Journal Letters.
Luhman stumbled across the third speedy star, called "source x,"
while he was hunting for free-floating planets in the Orion Nebula as a
member of an international team led by Massimo Robberto of the Space
Telescope Science Institute in Baltimore, Maryland. The team used the
near-infrared vision of Hubble's Wide Field Camera 3 to conduct the
survey. During the analysis, Luhman was comparing the new infrared
images taken in 2015 with infrared observations taken in 1998 by the
Near Infrared Camera and Multi-Object Spectrometer (NICMOS). He noticed
that source x had changed its position considerably, relative to nearby
stars over the 17 years between Hubble images, indicating the star was
moving fast, about 130,000 miles per hour.
The astronomer then looked at the star's previous locations,
projecting its path back in time. He realized that in the 1470s source x
had been near the same initial location in the Kleinmann-Low Nebula as
two other runaway stars, Becklin-Neugebauer (BN) and "source I."
BN was discovered in infrared images in 1967, but its rapid motion
wasn't detected until 1995, when radio observations measured the star's
speed at 60,000 miles per hour. Source I is traveling roughly 22,000
miles per hour. The star had only been detected in radio observations;
because it is so heavily enshrouded in dust, its visible and infrared
light is largely blocked.
The three stars were most likely kicked out of their home when they
engaged in a game of gravitational billiards, Luhman said. What often
happens when a multiple system falls apart is that two of the member
stars move close enough to each other that they merge or form a very
In either case, the event releases enough gravitational
energy to propel all of the stars in the system outward. The energetic
episode also produces a massive outflow of material, which is seen in
the NICMOS images as fingers of matter streaming away from the location
of the embedded source I star.
Future telescopes, such as the James Webb Space Telescope, will be
able to observe a large swath of the Orion Nebula. By comparing images
of the nebula taken by the Webb telescope with those made by Hubble
years earlier, astronomers hope to identify more runaway stars from
other multiple-star systems that broke apart.
The Hubble Space Telescope is a project of international cooperation
between NASA and ESA (European Space Agency). NASA's Goddard Space
Flight Center in Greenbelt, Maryland, manages the telescope. The Space
Telescope Science Institute (STScI) in Baltimore conducts Hubble science
operations. STScI is operated for NASA by the Association of
Universities for Research in Astronomy, Inc., in Washington, D.C.