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…]

Bathing asteroids with nuclear weapons

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

A gentle nudge with a nuke: deflecting Earth-bound asteroids

From Ars Technica:

In 2013, a small asteroid exploded in the atmosphere over Chelyabinsk, Russia. The sonic boom from the event sent more than a thousand people to the hospital, mostly from flying glass from shattered windows. The Chelyabinsk meteor was a relatively small chunk of space rock—asteroid researchers think it was probably about 20 meters (66 feet) across—but exploding over a city made it a noteworthy event. It’s probable many similar asteroids hit Earth on a regular basis, but most don’t happen to fly over metropolitan areas; they fall into the ocean or over lightly populated regions.

However, Earth has played target in the cosmic darts tournament before. Meteor Crater in Arizona, the Tunguska impact in Siberia in 1908, and most famously the Chicxulub asteroid in Mexico (which played a part in the extinction of the dinosaurs) are just three of many known examples. That’s why many people are looking at viable options for planetary defense: destroying or turning asteroids aside before they can hit Earth. And planetary defense is one reason the United States’ National Nuclear Safety Administration (NNSA) has given for not destroying some of its surplus nuclear warheads. [Read the rest at Ars Technica…]

Captain Picard may be a little confused.

Today, researchers with the LHCb experiment at CERN announced the confirmation of a weird object that first appeared in detectors in 2008. This object is made up of four quarks, where other particles are made of two or three quarks (or zero, in the case of electrons, neutrinos, and the like). But what sort of beast is this? As is often the case, more work is needed before we can say for ccertain.

With that much data, physicists were able to determine the composition of the Z(4430): it consists of a charm quark, a charm anti-quark, a down quark, and an up antiquark. The “4430” part of the name indicates its mass: 4,430 million electron-volts, which a little more than four times the mass of a proton (938 million electron volts). The combination of quarks gives the Z(4430) a negative electric charge, hence the “-” in the label. The particle is highly unstable, so none of them are expected to be seen in nature. [Read more…]

Four quarks for Muster Mark!

The particles of the the Standard Model and its simplest supersymmetric version. [Credit:  Pauline Gagnon]

The particles of the the Standard Model and its simplest supersymmetric version. [Credit:
Pauline Gagnon]

Symmetry and elegance have proven to be a very successful way to think about the physical Universe. Arguably the greatest successes in 20th century particle physics came from translating mathematical symmetries into predictions about the results of particle collisions. However, not every symmetry thus far has led to a successful theory, and one of the frustrations is that a natural consequence of a symmetry in the theory of relativity hasn’t produced the predicted particles. The currently unfulfilled theory is known as supersymmetry (or SUSY), and so far none of its predictions have borne out experimentally.

However, a completely analogous version of SUSY could exist in certain exotic superconductors. This is not built out of elementary particles, but out of interactions between electrons and atoms, giving rise to a set of particle-like quantum excitations known as quasiparticles.

The new paper discussed the idea of emergent SUSY-like behavior in topological superconductors. In these systems (described in more detail in the sidebar story), the interior of the material conducts electricity without resistance, but the outside is an ordinary conductor. The authors argued that experimentally observed magnetic behavior on the conducting surface could be interpreted super symmetrically. It also exhibits a breaking of SUSY due to the fundamental difference in interior and surface behavior of the system.

In this view, the magnetic excitations (acting like bosons) on the surface are SUSY partners with the topological superconductor quasiparticles, which are fermions. [read more…]

Supersymmetry in…superconductors?

The BICEP2 telescope (foreground) with the South Pole Telescope (SPT) behind. [Credit: Steffen Richter (Harvard University)]

The BICEP2 telescope (foreground) with the South Pole Telescope (SPT) behind. [Credit: Steffen Richter (Harvard University)]

Today was an exciting and stimulating day: the BICEP2 collaboration announced the first measurement of the cosmic microwave background that might tell us whether or not inflation happened. Inflation is the hypothetical rapid expansion of the Universe during its first instants, which explains a lot about why the cosmos appears the way it does. However, data on inflation itself, as opposed to its side-effects, are hard to come by. This new observation could help resolve that…assuming we can figure out why some of its aspects don’t agree with prior observations.

While they do not constitute a direct detection of either primordial gravitational waves (the distortions causing the light polarization) or inflation, the BICEP2 results could provide the best evidence for both that could not be easily explained away by other theories. This observation cannot be the end of the story, however. The measurement of polarization is significantly larger that what is seen in the results of prior observations in a way that cannot be immediately dismissed. Whether the problems are with the interpretation and analysis of the BICEP2 data, or if something more subtle is at work, remains to be seen. [Read more….]

New data offer a peek into the Universe’s first instants

A visual representation of the "axis of evil": the  strange alignment of temperature fluctuations on the largest scales on the sky. [Credit: Craig Copi]

A visual representation of the “axis of evil”: the strange alignment of temperature fluctuations on the largest scales on the sky. [Credit: Craig Copi]

On the largest scales — far bigger than any galaxy or galaxy cluster — the Universe is remarkably smooth and regular. Tiny irregularities in the early cosmos are what gave rise to all the structures we see today, including us, but there’s another irregularity covering the whole sky. The Universe appears to be ever-so-slightly lopsided, an anomaly facetiously known as the “axis of evil”. Cosmologists are concerned with trying to understand whether the anomaly is a significant challenge to our understanding of some of the laws of physics, or whether it can be understood either as a new astronomical source or a random fluke based on the fact that the whole cosmos is much larger than our observable Universe.

In my latest feature article at Ars Technica, I explored why the “axis of evil” could be a big deal and how some physicists are trying to understand it.

The lopsidedness is real, but cosmologists are divided over whether it reveals anything meaningful about the fundamental laws of physics. The fluctuations are sufficiently small that they could arise from random chance. We have just one observable Universe, but nobody sensible believes we can see all of it. With a sufficiently large cosmos beyond the reach of our telescopes, the rest of the Universe may balance the oddity that we can see, making it a minor, local variation.

However, if the asymmetry can’t be explained away so simply, it could indicate that some new physical mechanisms were at work in the early history of the Universe. [Read more….]

The mystery of the lopsided Universe

Astronomers measured the rotation of a black hole from halfway across the Universe.

What, I need to say more?

Astronomers have now used gravitational magnification to measure the rotation rate of a supermassive black hole in a very distant galaxy. From four separate images of the same black hole, R.C. Reis, M.T. Reynolds, J.M. Miller, and D.J. Walton found it was spinning nearly as fast as possible. That likely means it was spun up by a small number of mergers with other black holes rather than a gradual increase from eating smaller amounts of mass.

This marks the first measurement of black hole rotation outside the local Universe…. [Read more]

Measuring black hole rotation halfway across the Universe