Tag: white dwarf

Astronomers detect white dwarf star with two faces

9:13 am

The uncertainty of science: Astronomers using ground-based telescopes have discovered a white dwarf star in which the surface chemistry of its two hemispheres are very different, one strongly dominated by hydrogen while the other instead dominated by helium.

The team used the Low Resolution Imaging Spectrometer (LRIS) on the Keck I Telescope to view Janus in optical wavelengths (light that our eyes can see) as well as the Near-Infrared Echellette Spectrograph (NIRES) on the Keck II Telescope to observe the white dwarf in infrared wavelengths. The data revealed the white dwarf’s chemical fingerprints, which showed the presence of hydrogen when one side of the object was in view (with no signs of helium), and only helium when the other side swung into view.

The article lists a lot of proposed explanations, most of which suggest the star’s magnetic field is acting to segregate the materials. All assume these observations are certain and that there is no mixing at all, something we should doubt considering the resolution of the data (a mere point that is rotating).

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Fragment of a long dead planet’s iron core found orbiting white dwarf

8:25 am

Astronomers have identified the fragment of a long dead planet’s iron core orbiting a white dwarf star 410 light years away.

The [data] suggested its source was a solid object some 600 kilometers across—a suspected planetary core, with a density between 7.7 and 39 grams per cubic meter, comparable to the pure iron found within Earth’s core. “The density of the piece of rock is consistent with what we think the cores of planets [are],” says Luca Fossati of the Austrian Academy of Sciences, who was not involved in the paper.

It orbits the star every two hours, the fastest exoplanet orbit yet found. This alone should rip it apart, providing further evidence that the object’s density is very high.

The astronomers theorize that this object is likely the remains of a planet that existed when this star was young, and was destroyed as the star aged to become a red giant, expanding to swallow it. Later, when the star collapsed to become a tiny white dwarf, the core remained, its density allowing it survive as the planet’s outer crust was torn away.

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A very old white dwarf star with rings?

10:19 am

The uncertainty of science: A citizen scientist has discovered a very old white dwarf star that apparently has one or more dust rings it should not have.

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.”

In other words, we don’t really yet understand the processes that form solar systems or even stars. This isn’t because we can’t figure this out, but because we don’t yet have enough information on hand. What we do know tells us that stars and solar systems both form from accretion disks. The information also gives us a general idea of the pattern of formation, but not much more.

For example, one question I have asked a number of astronomers is: Why are some stars gigantic monsters and others dwarfs? Based on present theories of stellar evolution, it seems to me that all stars should be the same size, as accretion is thought to end when the star reaches a heavy enough mass to ignite its nuclear engine. Yet this is not what we find. Why? I’ve never gotten a good answer.

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The supernova of a generation

12:00 pm

The supernova of a generation.

There will be a slew of stories about this in the next few days. The important takeaways are as follows:

  • After almost a half century, astronomers have finally proven the theory that type Ia supernovae come from the explosion of a white dwarf star, overloaded with material sucked from its binary companion.
  • The prediction that the companion would be a red giant star, however, has turned out to be wrong. At the same time, astronomers still do not know what kind of star it was in this particular case.
  • With this new knowledge astronomers will have a better chance of identifying type Ia supernovae, before they go boom.
  • Finally, type Ia supernovae are used to measure the expansion rate of the universe, and thus were the key to discovering dark energy. By better understanding how these supernovae occur, cosmologists will be better able to constrain what they know about dark energy.
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