In this illustration, an asteroid (bottom left)
breaks apart under the powerful gravity of LSPM J0207+3331, the oldest,
coldest white dwarf known to be surrounded by a ring of dusty debris.
Scientists think the system’s infrared signal is best explained by two
distinct rings composed of dust supplied by crumbling asteroids. Credits: NASA’s Goddard Space Flight Center/Scott Wiessinger. Download in high-resolution formats from NASA Goddard's Scientific Visualization Studio
Citizen scientists working on Backyard Worlds:
Planet 9 scrutinize “flipbooks” of images from NASA’s Wide-field
Infrared Survey Explorer. This animation shows a flipbook containing the
ring-bearing white dwarf LSPM J0207+3331 (circled). Credits: Backyard Worlds: Planet 9/NASA’s Goddard Space Flight Center
A volunteer working with the NASA-led Backyard Worlds: Planet 9
project has found the oldest and coldest known white dwarf — an
Earth-sized remnant of a Sun-like star that has died — ringed by dust
and debris. Astronomers suspect this could be the first known white
dwarf with multiple dust rings.
The star, LSPM J0207+3331 or J0207 for short, is forcing researchers
to reconsider models of planetary systems and could help us learn about
the distant future of our solar system.
“This white dwarf is so old that whatever process is feeding material
into its rings must operate on billion-year timescales,” said John
Debes, an astronomer at the Space Telescope Science Institute
in Baltimore. “Most of the models scientists have created to explain
rings around white dwarfs only work well up to around 100 million years,
so this star is really challenging our assumptions of how planetary
systems evolve.”
A paper detailing the findings, led by Debes, was published in the Feb. 19 issue of The Astrophysical Journal Letters and is now available online.
J0207 is located around 145 light-years away in the constellation Capricornus.
White dwarfs slowly cool as they age, and Debes’ team calculated J0207
is about 3 billion years old based on a temperature just over 10,500
degrees Fahrenheit (5,800 degrees Celsius). A strong infrared signal
picked up by NASA’s Wide-field Infrared Survey Explorer (WISE)
mission — which mapped the entire sky in infrared light — suggested the
presence of dust, making J0207 the oldest and coldest white dwarf with
dust yet known. Previously, dust disks and rings had only been observed
surrounding white dwarfs about one-third J0207’s age.
When a Sun-like star runs out of fuel, it swells into a red giant, ejects at least half of its mass, and leaves behind a very hot white dwarf.
Over the course of the star’s giant phase, planets and asteroids close
to the star become engulfed and incinerated. Planets and asteroids
farther away survive, but move outward as their orbits expand. That’s
because when the star loses mass, its gravitational influence on
surrounding objects is greatly reduced.
This scenario describes the future of our solar system.
Around 5
billion years from now, Mercury, then Venus and possibly Earth will be
swallowed when the Sun grows into a red giant. Over hundreds of
thousands to millions of years, the inner solar system will be scrubbed
clean, and the remaining planets will drift outward.
Yet some white dwarfs — between 1 and 4 percent — show infrared
emission indicating they’re surrounded by dusty disks or rings.
Scientists think the dust may arise from distant asteroids and comets
kicked closer to the star by gravitational interactions with displaced planets.
As these small bodies approach the white dwarf, the star’s strong
gravity tears them apart in a process called tidal disruption. The
debris forms a ring of dust that will slowly spiral down onto the
surface of the star.
J0207 was found through Backyard Worlds: Planet 9, a project led by
Marc Kuchner, a co-author and astrophysicist at NASA’s Goddard Space
Flight Center in Greenbelt, Maryland, that asks volunteers to sort
through WISE data for new discoveries.
Melina Thévenot, a co-author and citizen scientist in Germany working with the project, initially thought the infrared signal was bad data. She was searching through the ESA’s (European Space Agency’s) Gaia
archives for brown dwarfs, objects too large to be planets and too
small to be stars, when she noticed J0207. When she looked at the source
in the WISE infrared data, it was too bright and too far away to be a
brown dwarf. Thévenot passed her findings along to the Backyard Worlds:
Planet 9 team. Debes and Kuchner contacted collaborator Adam Burgasser
at the University of California, San Diego to obtain follow-up
observations with the Keck II telescope at the W. M. Keck Observatory in Hawaii.
“That is a really motivating aspect of the search,” said Thévenot,
one of more than 150,000 citizen scientists on the Backyard Worlds
project. “The researchers will move their telescopes to look at worlds
you have discovered. What I especially enjoy, though, is the interaction
with the awesome research team. Everyone is very kind, and they are
always trying to make the best out of our discoveries.”
The Keck observations helped confirm J0207’s record-setting
properties. Now scientists are left to puzzle how it fits into their
models.
Debes compared the population of asteroid belt analogs in white dwarf
systems to the grains of sand in an hourglass. Initially, there’s a
steady stream of material. The planets fling asteroids inward towards
the white dwarf to be torn apart, maintaining a dusty disk. But over
time, the asteroid belts become depleted, just like grains of sand in
the hourglass. Eventually, all the material in the disk falls down onto
the surface of the white dwarf, so older white dwarfs like J0207 should
be less likely to have disks or rings.
J0207’s ring may even be multiple rings. Debes and his colleagues
suggest there could be two distinct components, one thin ring just at
the point where the star’s tides break up the asteroids and a wider ring
closer to the white dwarf. Follow-up with future missions like NASA's James Webb Space Telescope may help astronomers tease apart the ring’s constituent parts.
“We built Backyard Worlds: Planet 9 mostly to search for brown dwarfs
and new planets in the solar system,” Kuchner said. “But working with
citizen scientists always leads to surprises. They are voracious — the
project just celebrated its second birthday, and they’ve already
discovered more than 1,000 likely brown dwarfs. Now that we’ve rebooted
the website with double the amount of WISE data, we’re looking forward
to even more exciting discoveries.”
Backyard Worlds: Planet 9 is a collaboration between NASA, the
American Museum of Natural History in New York, Arizona State
University, National Optical Astronomy Observatory, the Space Telescope
Science Institute in Baltimore, the University of California San Diego,
Bucknell University, the University of Oklahoma, and Zooniverse, a
collaboration of scientists, software developers and educators who
collectively develop and manage citizen science projects on the
internet.
NASA's Jet Propulsion Laboratory in Pasadena, California, manages and
operates WISE for NASA's Science Mission Directorate. The WISE mission
was selected competitively under NASA's Explorers Program managed by the
agency's Goddard Space Flight Center. The science instrument was built
by the Space Dynamics Laboratory in Logan, Utah. The spacecraft was
built by Ball Aerospace & Technologies Corp. in Boulder, Colorado.
Placed in hibernation in 2011, the spacecraft was reactivated in 2013
and renamed NEOWISE. Science operations and data processing take place
at the Infrared Processing and Analysis Center at Caltech, which manages
JPL for NASA.
For more information about Backyard Worlds: Planet 9, visit: http://backyardworlds.org
For more information about NASA's WISE mission, visit: http://www.nasa.gov/wise
Editor: Rob Garner
Source: NASA/Stars
