Blowing up high-mass stars with low-mass neutrinos

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Low-mass particles that make high-mass stars go boom

Simulations are key to showing how neutrinos help stars go supernova.

For Symmetry Magazine:

When some stars much more massive than the sun reach the end of their lives, they explode in a supernova, fusing lighter atoms into heavier ones and dispersing the products across space—some of which became part of our bodies. As Joni Mitchell wrote and Crosby Stills Nash & Young famously sang, “We are stardust, we are golden, we are billion-year-old carbon.”

However, knowing this and understanding all the physics involved are two different things. We can’t make a true supernova in the lab or study one up close, even if we wanted to. For that reason, computer simulations are the best tool scientists have. Researchers program equations that govern the behavior of the ingredients inside the core of a star to see how they behave and whether the outcomes reproduce behavior we see in real supernovae. There are many ingredients, which makes the simulations extraordinarily complicated—but one type of particle could ultimately drive supernova explosion: the humble neutrino. [Read the rest at Symmetry Magazine]


The Cassiopeia A supernova remnant. [Credit: NASA/CXC/SAO]

The Cassiopeia A supernova remnant. [Credit: NASA/CXC/SAO]

Nearly every atom of your body was forged in a supernova explosion and dispersed into space. But how do massive stars explode? The details are complicated, pushing the limits of computer simulations and our ability to observe with telescopes. In the absence of very close-by events, the best data come from supernova remnants: the still-glowing gas ejected during the explosion. A new set of observations of X-ray emissions from radioactive titanium in the Cassiopeia A supernova remnant show that it was a lumpy space princess highly asymmetrical explosion. That agrees with theory, but the researchers also turned up an odd disconnect between the titanium and other materials.

Cassiopeia A (abbreviated Cas A) is a historical oddity. The supernova was relatively close to Earth—a mere 11,000 light-years distant—and should have been visible around CE 1671, yet no astronomers of any culture recorded it. That’s in stark contrast to famous earlier explosions: Tycho’s supernova, Kepler’s supernova, and of course the supernova that made the Crab Nebula. This mysterious absence has led some astronomers to speculate that some unknown mechanism diffused the energy from the explosion, making the supernova far less bright than expected. [Read more…]

Supernovas: mysterious and lumpy space explosions

The week in review (October 13 – 19)

I’m at GeekGirlCon this weekend, so I’m busy with non-writing activities as part of the DIY Science Zone. Thanks to our Fearless Leader Dr. “Nick Fury” Rubidium for putting our part of the event together!

  • Where Nature Hides the Darkest Mystery of All (Nautilus): Even though there’s no solid barrier, the event horizon of a black hole provides a boundary through which we can’t see or probe. That leads to a troubling idea: will we ever know what’s really inside that event horizon? Is there any way to learn about the interior by indirect measurements?
  • Black hole hair and the dark energy problem (Galileo’s Pendulum): Building off that article, what happens if our standard theory of gravity is modified? That’s not an entirely crazy idea: several modifications to general relativity have been proposed, inspired by inflation (the rapid expansion during the cosmos’ earliest moments) or dark energy. A recent paper examined that idea, and here’s my take.
  • Strongly magnetic pulsar could explain anomalous supernovas (Ars Technica): Some supernovas are particularly bright, especially some from the early Universe. These, known as “pair-instability” supernovas, are the explosion of very massive stars made of nearly pure hydrogen and helium. However, some of these super-luminous supernovas don’t quite fit that profile, including being too close. A new set of observations may show they are actually driven by a magnetar, a highly magnetized pulsar.
  • Gravitational waves show deficit in black hole collisions (Ars Technica): Mergers of supermassive black holes should happen frequently enough to produce a bath of gravitational radiation permeating the cosmos. While that gravitational wave background (GWB) possesses wavelengths too large for ground-based detectors like LIGO, astronomers realized it might be visible in the fluctuations of light from pulsars. However, they didn’t see what they expected, leading to the big question: why not?

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

Any core-collapse supernova—the explosion of a massive star—is by nature powerful, destructive, and rare. The really dramatic supernovas have the extra effect of exploding in a non-spherical way, beaming a lot of their matter and energy along an axis. When Earth is aligned with those beams, we see the supernova as a gamma ray burst (GRB), the brightest of which can be seen from billions of light-years away. (As the name suggests, these events are exceptionally bright in gamma ray light. In fact, they were first discovered by spy satellites monitoring for illicit nuclear tests—which are also marked by heavy gamma ray emission.) Observations of a supernova remnant in our galaxy strongly hint both that it was a GRB, and that it harbors a black hole at its center. That would mean the supernova is the only known GRB in our galaxy, and its black hole is the youngest known—a wonderful double discovery.

While stars like our Sun go gently into that good night, stars more than 25 times more massive explode in violent supernovae. Since stars that big are rare, their explosions are too, so astronomers typically have to do forensic work on supernova remnants in our galaxy. One particular remnant is one the brightest X- and gamma-ray sources around, marking it as a relatively recent explosion. By studying the remnant, astronomers have determined it likely harbors the youngest black hole in the Milky Way, and the original explosion may have been extremely energetic. [Read more…]

Weird supernova marks the spot of a violent outburst…and black hole

(Yes, I’m inundating you all with writing. It’s a busy week, and I still have a few more things forthcoming to share with you.)

Supernova remnant SNR 1987a, what’s left after a bright blue star exploded in the Large Magellanic Cloud. [Credit: NASA/ESA/P. Challis and R. Kirshner (Harvard-Smithsonian Center for Astrophysics]

Supernova 1987a was the death of a massive blue star in the Large Magellanic Cloud, one of the satellite galaxies of our Milky Way. Because of its relative proximity and occurrence during the era of modern astronomy, the supernova remnant SNR 1987a (as it is known) is one of the best-studied of all. As a result, it provides a good testbed for the theory of star explosions. A new X-ray observation has measured the amount of radioactive titaniumcreated in the remnant, and showed it’s enough to power a lot of the light emission in the years following the supernova.

The decay of 44Ti produces high-energy X-ray photons at three distinct wavelengths. The researchers in the current study aimed the INTEGRAL (INTErnational Gamma-RAy Laboratory) satellite at SNR 1987a for about 4.5 million seconds (a total of over seven weeks) to obtain clear X-ray spectra. This process was complicated by the presence of a pulsar and a black hole binary system that, from our perspective, appear near SNR 1987a in the sky—these bodies also emit X-ray light. The astronomers identified the telltale spectral signature of titanium decay, and extrapolated from the number of photons (the flux) to determine the mass of the titanium before the decay process began. [Read more….]

Radioactive titanium powers a supernova afterglow