Learning about weird star corpses from the way they shake

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‘Dwarfquakes’ Reveal the Future of Our Universe

Dying stars were an enigma—until an astronomer measured seismic shifts on them, giving us clues about the sun’s future and the expansion rate of the universe.

For The Daily Beast:

White dwarfs—the hot, burned-out remains of ordinary stars—are very common in the universe, and weird. (Our very own sun will become a white dwarf in a few billion years, too.) Imagine something the size of Earth, but 300,000 times more massive, glowing white-hot and bright enough to be seen far away despite its tiny size.

“It’s just a pixel of light,” Noemi Giammichele, an astronomer at the University of Toulouse, told The Daily Beast. “I find it really amazing all the information we can gather just from that one tiny dot.”

Made of pure carbon and oxygen, with only a thin haze of other atoms acting as its atmosphere, white dwarfs certainly aren’t like anything we can make in a lab on Earth. But Giammichele used seismology to measure “dwarfquakes” to not only understand the internal structure of these white dwarfs but also the future expansion rate of our universe.

[Read the rest at The Daily Beast]

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Listening to the sounds of the cosmos

[ This blog is dedicated to tracking my most recent publications. Subscribe to the feed to keep up with all the science stories I write! ]

Last year, I went to a conference in Florida to hear — and in some cases meet — some of the leading thinkers in the study of gravitational waves. These waves are disturbances in the structure of spacetime itself, and could provide information about some exciting phenomena, if we can learn to detect them. The universe as heard in gravitational waves includes colliding black holes, white dwarfs locked in mutual orbits, exploding stars, and possibly chaotic disturbances from the very first instants after the Big Bang. This story marks one of my first big magazine articles, which I wrote for Smithsonian Air & Space magazine.

The Universe is Ringing

And astronomers are building observatories to listen to it

For Smithsonian Air & Space:

Think of it as a low hum, a rumble too deep to notice without special equipment. It permeates everything—from the emptiest spot in space to the densest cores of planets. Unlike sound, which requires air or some other material to carry it, this hum travels on the structure of space-time itself. It is the tremble caused by gravitational radiation, left over from the first moments after the Big Bang.

Gravitational waves were predicted in Albert Einstein’s 1916 theory of general relativity. Einstein postulated that the gravity of massive objects would bend or warp space-time and that their movements would send ripples through it, just as a ship moving through water creates a wake. Later observations supported his conception. [Read the rest at Air & Space….]

A white dwarf murder mystery

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What killed the white dwarfs? (Aside from the giant explosion)

Merger or extra matter? Two papers come to opposite conclusions

For Ars Technica:

Type Ia supernovae are explosions that occur when white dwarfs strip matter off a companion star, exceed their maximum possible mass, and blow up.

No, wait: type Ia supernovae are the explosions caused when two white dwarfs collide.

While it’s reasonably certain that white dwarfs—the Earth-size remnant of stars similar to the Sun—are involved, the observational evidence for how these supernovae actually explode is messy. This week’s issue of Nature is a prime example: two back-to-back papers provide evidence for a white dwarf-companion star explosion and a two-white-dwarf collision scenario, respectively. Ultimately, these apparently contradictory results could mean there are two distinct types of white dwarf supernovae… or that we still don’t understand what’s going on.

The stakes are high. Unlike other supernovae, which involve the death of a star much more massive than the Sun, type Ia supernovae all explode in very similar ways. The pattern of light they emit during and after the explosion provides a reliable measurement of how far away they are. Since supernovae are bright enough to be visible from billions of light-years away, astronomers use them to measure the expansion and acceleration rate of the Universe, as recognized in the 2011 Nobel Prize in physics. Because they are so important to cosmology, researchers want to understand what objects are involved in the explosion and exactly how they blow up. [Read the rest at Ars Technica…]

General relativity holds up under extreme gravity test

The general theory of relativity is the reigning champion of gravitational theories: it’s withstood tests in the Solar System, near black holes, and in binary systems. Most recently, astronomers performed detailed observations of a pulsar-white dwarf binary system, which provided an exquisite example of general relativity in action. Pulsars and white dwarfs are both the remnants of stars, but pulsars in particular are interesting: they pack the mass of a star into a sphere about 20 kilometers across. That means the gravity at the surface of a pulsar is extreme, so when one is in a binary system, it provides a laboratory for measuring strong gravitational effects.

The pulsar itself was interesting because of its relatively high mass: about 2.0 times that of the Sun (most observed pulsars are about 1.4 times more massive). Unlike more mundane objects, pulsar size doesn’t grow with mass; according to some models, a higher mass pulsar may actually be smaller than one with lower mass. As a result, the gravity at the surface of PSR J0348+0432 is far more intense than at a lower-mass counterpart, providing a laboratory for testing general relativity (GR). The gravitational intensity near PSR J0348+0432 is about twice that of other pulsars in binary systems, creating a more extreme environment than previously measured. [Read more…]

Also, let the record show: it’s possible to write an article about testing general relativity without mentioning Einstein, much less making the story about “proving him right” (or wrong).

White dwarfs are the remnants of the cores of stars like our Sun. They have the mass of a star packed into the volume of Earth, but when they die, their light can be detected across the observable Universe. Researchers using the Hubble Space Telescope identified the farthest white dwarf supernova yet seen, one which exploded more than 10 billion years ago.

Only 8 white dwarf supernovas have been identified farther than 9 billion light-years away. (Some core-collapse supernovas, which are the explosions of very massive stars, have been seen farther than Supernova Wilson.) Since all such explosions happen in a similar way, cosmologists use them to measure the expansion rate of the Universe. [Read more…]

I gotta say, though: this supernova was nicknamed “Woodrow Wilson”, which kind of bugs me. Wilson was a war president, which means we Americans tend to give him a pass on a lot of things, but both his foreign and domestic policies reeked of racism. He worked against racial equality at home and abroad, stamping on egalitarian movements in the League of Nations and segregating the Federal Government. (The previous Republican administrations, for all their faults, had been making efforts to give African-Americans a voice after the Civil War.) Anyway, that’s mostly beside the point. If you want to read about a supernova named for someone whose work I do admire (prickly though he was), see my post about Supernova Mingus.

Death of a white dwarf, 10 billion years later

White dwarf supernovas—more officially known as type Ia supernovas—are important to cosmologists because they all explode in very similar ways. That means they can be used to measure distances to faraway galaxies. However, a peculiar type of supernova, first identified in 2002, has a lot in common with type Ia explosions, but with a lot less energy. Some astronomers are now saying this could be a new class of white dwarf supernova that produces much less light and sends material into interstellar space at far lower speeds.

Beginning in 2002, astronomers started recognizing a peculiar type of explosion. Since then, they’ve identified 25 of them; they resemble white dwarf supernovas in many respects, but strongly differ in others. A new paper by Ryan J. Foley and colleagues offered an explanation: these were an entirely new type of white dwarf explosion, one involving less energy and more material from a companion star. So much less energy, in fact, that the authors suspect that the white dwarf may not be fully destroyed in these odd events. [Read more…]

Baby boom-ers could be a new type of white dwarf supernova

Eta Carinae, one of the best candidates for going supernova in our lifetimes - assuming we understand the physics of the system, which we don't. [Credit:  NASA, ESA, and the Hubble SM4 ERO Team]Supernovas are some of the most violent phenomena in the cosmos, but we’re in no immediate danger from one. However, astronomers would really really really like one to go off relatively nearby during our lifetimes, since we would learn a lot from observing one. My latest piece at Ars Technica is a gallery showing some of the more interesting supernova candidates in our galaxy, including a few that might possibly go kaboom while I’m still around to see it happen.

Supernovas and Marvin the Martian