Nav: Home

Contracting white dwarf observed for the first time

November 14, 2017

Astrophysicists from MSU (Russia) and his colleagues from Italy and Russian Academy of Sciences have found the first observational evidence for a contracting white dwarf. Constant high spin-up rate of a star of this type, located in an enigmatic binary system, can be easily explained if the white dwarf is contracting, the researchers argue. The discovery is reported in the Monthly Notices of the Royal Astronomical Society.

"Thanks to this discovery, astrophysicists will be able to study and evaluate the evolution patterns of young white dwarfs -- and successfully look for similar systems in the galaxy, " -- noted the main author of the article, astrophysicist Sergei Popov (SAI MSU).

It is widely believed, based on theoretical considerations, that young white dwarfs -- the compact remnants of solar-like stars, -- should experience a phase of contraction in their early life. The radius of a typical white dwarf can decrease by several hundred kilometers during the first million years of its life. However, there was no observational evidence for this effect up to now. First, because most of the known white dwarf are much older. Second, because the scientists do not have a direct and precise way to measure the radii, and their variations, in these stars.

Studying an enigmatic X-ray source in a binary system of a rare type, the scientists might have found the first observational evidence for a contracting white dwarf. The binary system HD49798/RX J0648.0-4418 is at a distance of 2000 light years, in the Puppis constellation, and has been extensively studied with optical, UV, and X-ray telescopes. It contains a massive white dwarf, which spins with a period of only 13 s, the fastest known for a white dwarf, and emits X-rays due to the accretion of matter captured from the stellar wind of its companion star.

Sandro Mereghetti (a coauthor of the new paper) recently discovered that the rotational velocity of this white dwarf has been steadily increasing during the latest 20 years. Its spin period of 13 s is decreasing by 7 nanoseconds every year. This might seem a very small change, but it is actually a very large effect for a body weighting more than our Sun, but with a radius as small as about 5000 km (less than the Earth). Indeed, such a large spin-up rate could not be easily explained in standard ways (e.g. by the captured angular momentum of the accreting matter).

The solution to this puzzle has been now presented by the authors of this new study. They demonstrate that the high spin-up rate can be easily explained if the white dwarf is contracting, exactly as in the case of a spinning skater that brings in her arms to rotate faster. The evolutionary calculations presented in the paper show that the white dwarf has an age of only about 2 million years. The contraction rate of about one centimeter per year expected for this age is exactly of the correct amount to explain the measured spin-up rate, showing that this is the first example of contracting white dwarf ever identified.

"For decades it has been theoretically clear that that young white dwarfs are contracting. Yet, that very phase of contraction has never been observed "in real time". We should thank the uniqueness of the binary system under study: the white dwarf was literally illuminated (due to the accretion of matter from the neighboring star). But it was highlighted so neatly that the accreting matter did not affect its rotation -- an extremely rare phenomenon! In other similar systems, accretion is much more powerful: it determines how the white dwarf rotates, which makes it impossible to notice the beauty of contraction", - Popov explained.
-end-


Lomonosov Moscow State University

Related White Dwarf Articles:

New way to weigh a white dwarf: Use Hubble Space Telescope
For the first time, astronomers have used a novel method to determine the mass of a type of star known as a 'white dwarf' -- the shrunken corpse of a dead star that used to be like our sun.
Hubble astronomers use a century-old relativity experiment to measure a white dwarf's mass
Astronomers have used the sharp vision of NASA's Hubble Space Telescope to repeat a century-old test of Einstein's general theory of relativity.
Hubble spots moon around third largest dwarf planet
Astronomers uncovered a moon orbiting the third largest dwarf planet, 2007 OR10, in the frigid outskirts of our solar system called the Kuiper Belt.
Surprise! When a brown dwarf is actually a planetary mass object
Sometimes a brown dwarf is actually a planet -- or planet-like anyway.
Astronomers identify purest, most massive brown dwarf
An international team of astronomers has identified a record breaking brown dwarf (a star too small for nuclear fusion) with the 'purest' composition and the highest mass yet known.
Ultracool dwarf and the 7 planets
Astronomers have found a system of seven Earth-sized planets just 40 light-years away.
Hubble witnesses massive comet-like object pollute atmosphere of a white dwarf
For the first time, scientists using NASA's Hubble Space Telescope have witnessed a massive object with the makeup of a comet being ripped apart and scattered in the atmosphere of a white dwarf, the burned-out remains of a compact star.
Hubble finds big brother of Halley's Comet ripped apart by white dwarf
Scientists using the NASA/ESA Hubble Space Telescope have observed, for the first time, a massive, comet-like object that has been ripped apart and scattered in the atmosphere of a white dwarf.
Dwarf star 200 light years away contains life's building blocks
Many scientists believe the Earth was initially dry and that water, carbon and nitrogen -- the building blocks for life -- likely came as a result of collisions with objects that began their lives in the cold outer reaches of our solar system.
Mysterious white dwarf pulsar discovered
An exotic binary star system 380 light-years away has been identified as an elusive white dwarf pulsar -- the first of its kind ever to be discovered in the universe -- thanks to research by the University of Warwick.

Related White Dwarf Reading:

White Dwarf
by Warren Mann (Author)

Snow White and the Seven Dwarfs: The Story of Snow White (Disney Princess)
by Disney Book Group (Author), Disney Storybook Art Team (Illustrator)

Snow White and the Seven Dwarfs: The Art and Creation of Walt Disney's Classic Animated Film
by J.B. Kaufman (Author)

Snow White and the Seven Dwarfs (Disney Classic) (Little Golden Book)
by RH Disney (Author), RH Disney (Illustrator)

Snow White and the Seven Dwarfs: The Classics Read by Celebrities
by Blackstone Audio, Inc.

Snow-White and the Seven Dwarfs: A Tale from the Brothers Grimm (Sunburst Book)
by Jacob Grimm (Author), Wilhelm K. Grimm (Author), Nancy Ekholm Burkert (Illustrator), Randall Jarrell (Illustrator)

Snow White and the Seven Dwarfs (Read-Along Storybook and CD)
by Disney Storybook Art Team (Illustrator)

Unlocking the Secrets of White Dwarf Stars (Astronomers' Universe)
by Hugh M. Van Horn (Author)

Walt Disney's Snow White and the Seven Dwarfs
by Cynthia Rylant (Author), Gustaf Tenggren (Illustrator)

Snow White and the 77 Dwarfs
by Davide Cali (Author), Raphaelle Barbanegre (Illustrator)

Best Science Podcasts 2018

We have hand picked the best science podcasts for 2018. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Hacking The Law
We have a vision of justice as blind, impartial, and fair — but in reality, the law often fails those who need it most. This hour, TED speakers explore radical ways to change the legal system. Guests include lawyer and social justice advocate Robin Steinberg, animal rights lawyer Steven Wise, political activist Brett Hennig, and lawyer and social entrepreneur Vivek Maru.
Now Playing: Science for the People

#495 Earth Science in Space
Some worlds are made of sand. Some are made of water. Some are even made of salt. In science fiction and fantasy, planet can be made of whatever you want. But what does that mean for how the planets themselves work? When in doubt, throw an asteroid at it. This is a live show recorded at the 2018 Dragon Con in Atlanta Georgia. Featuring Travor Valle, Mika McKinnon, David Moscato, Scott Harris, and moderated by our own Bethany Brookshire. Note: The sound isn't as good as we'd hoped but we love the guests and the conversation and we wanted to...