SEATTLE -
Dust shed by a dying star is being
siphoned by its healthy companion to build new planets, a new study suggests.
Located 350
light-years away in the constellation Cetus, Mira A is a massive, bloated red
giant star that was once very similar to our Sun.
It is now in its final stages and on its way to becoming a stellar corpse known
as a white
dwarf, a process that will take about a million years.
As part of
this transformation, Mira A is shedding its outer layers of dust, at a rate of
about one Earth-mass every seven
years [image].
Normally, this material would diffuse into outer space.
Captured
instead
But using
the Keck I telescope in Hawaii and the Gemini South telescope in Chile,
researchers have discovered that about 1 percent of this dust is being
gravitationally captured by Mira A's companion, Mira B. The two stars are
separated by a distance of about 90 AU. One AU, or astronomical unit, is equal
to the distance between the Earth and the Sun [image].
Mira A's
dust is settling into a ring around Mira B, a less massive version of our own
Sun, and could eventually serve as the building material for new planets. The
shed star dust consists mostly of silicate, the same material that makes up the
Earth's mantle.
"This
is a new type of planetary disk that is born when a companion star dies,"
said study team member Michael Ireland of Caltech. "At the moment, the
disk is probably less than a Jupiter-mass in size. But over the lifetime of
Mira A, it's going to accrete three to five times the mass of Jupiter."
The
researchers spotted Mira B's disk because the part of the disk facing Mira A glowed
brightly in the infrared, heated by radiation from the red giant. Ireland
presented his team's findings here this week at the 209th meeting of
the American Astronomical Society.
Death
meant death
Astronomers
used to think that the death of a star meant the death of its planets, but in
the case of Mira A, an "aging star is laying the foundation for a new
generation of planets," Ireland said.
"This
discovery opens up a new way to search for young planets, by searching in
double star systems that contain white dwarfs," Ireland said. "The
expected abundance of these systems means that we can find planets that we know
are young around stars like our Sun."
If planets
were to form around Mira B, and life developed on those planets, radiation from
Mira A is not expected to pose a threat once enough time passes.
"It
would pose a problem for life forms during the planetary formation process,
while the white dwarf is still very young. But the white dwarf cools very
quickly," Ireland said.
When Mira A
contracts into a white dwarf, it will be about the size of the Earth, separated
from Mira B by a distance equal to that between Earth and Pluto, and it will
shine less brightly than a full Moon in our night skies.
"It
won't affect life," Ireland said.
Editor's
Note: All
week, SPACE.com is providing complete
coverage of the 209th meeting of the American Astronomical Society.
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