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…]
Type Ia supernovae are triggered either by the explosion of white dwarfs that accrete too much matter and exceed their maximum stable mass, or by the collision of two white dwarfs. (That’s as opposed to core-collapse supernovae, which are the explosions of stars much more massive than the Sun.) Because they all explode in very similar ways, Type Ia supernovas are “standard candles”: objects that can be used to measure distances to very distant galaxies. The use of them to track the expansion of the Universe was recognized by the 2011 Nobel Prize. [read more…]
What’s cool is that various astronomers, including a number of amateur astronomers, spotted the supernova before it was identified as such. M82 is a popular observing target because it’s distinctive and (yes) not far away. My colleagues at Universe Today and CosmoQuest actually highlighted the galaxy during their Virtual Star Party on Sunday evening, meaning they saw the supernova before we knew what a big deal it was going to be!
Most galaxies are somewhat red or blue in appearance, depending on the populations of stars that comprise them. However, citizen scientists working with the GalaxyZoo project identified a previously unknown type of galaxy: Green Peas, so named because they are small and green. The color comes from ionized oxygen, a particular form of emission that only happens under unusual conditions. A new study shows that Green Peas could resemble a kind of early galaxy responsible for reionization: the breakdown of atoms due to aggressive star formation when the Universe was young.
A new paper by A. E. Jaskot and M. S. Oey argues that galaxies much like the Green Peas could be responsible for the reionizing radiation. They analyzed the light emissions from the galaxies, and determined that their gas is thinner than in typical star-forming galaxies, which could allow more ultraviolet light into intergalactic space. The researchers also found signs in a few Green Peas of extremely massive stars, the ones most responsible for ionizing radiation. [Read more…]
A mystery: an unknown star, too faint to notice, suddenly expanded to a huge size, increasing in brightness to become one of the most luminous stars known. This star doesn’t even have a real name, just a “license plate” catalog number: V838 Monocerotis, indicating that it’s a not very important star in the constellation the Unicorn (Monoceros). However, a new paper has proposed the powerful flare could be explained by a well-accepted theory of binary star behavior, in which one star strips enough matter off the other until it suddenly grows to a huge size. These common envelope events (as they are known) could explain the V838 Monocerotis outburst, along with some other currently mysterious flares.
A new Science paper proposes that a class of violent astronomical events that we’ve observed may be due to common envelope stars, providing more direct evidence for their existence. These cataclysms are known as “red transient outbursts,” and in brightness terms, they’re somewhere between novas (flares of nuclear activity at the surfaces of white dwarfs) and supernovas, the violent deaths of stars. N. Ivanova, S. Justham, J. L. Avendado Nandez, and J. C. Lombardi Jr. identified a possible physical model for these outbursts, based on the recombination of electrons and ions in the plasma when the stars’ envelopes merge. [Read more…]
Every exoplanet discovery seems to bring us closer to understanding the variety of planetary systems out there in our galaxy. The latest find is particularly exciting: an Earth-mass planet orbiting around Alpha Centauri B, one of three stars in the closest system to the Solar System. The planet isn’t very Earthlike in most respects, but it’s still an incredibly exciting discovery.
However, the discovery is still exciting for a number of reasons. First is the proximity of the star system to us: Alpha Centauri is 4.4 light years away, a tiny distance in cosmic terms. The stars Alpha Centauri A and B are some of the brightest in the sky in the Southern Hemisphere. (Sorry, fellow Northern Hemisphere-dwellers; we can’t see them from here.) We don’t have starship technology to travel there, but we could conceivably send a robotic probe that could arrive within my lifetime, and 4.4 years isn’t a terribly long time for data to travel back to Earth. No one has such a probe in the works yet, but the mere fact of discovery of a planet might encourage investment in that direction. [Read more…]
Though it may seem sad on the surface, the death of a star is a beautiful thing—and an important precursor to the birth of new stars and planets. The Atacama Large Millimeter Array (ALMA) in Chile has provided a breathtaking view of a star nearing the end of its life. One unexpected feature was a lovely spiral pattern that probably indicates the presence of a hidden companion.
While earlier observations showed a thin spherical shell of gas perfectly centered on R Sculptoris, the ALMA data revealed unexpected structure inside. The details included clumps in the gas shell and a winding spiral pattern, as seen in the image above. Additionally, the amount of mass contained in the surrounding matter is approximately three times what was estimated from earlier observations and models of similar stars. [Read more….]
(This headline was my original choice for the article, which was understandably rejected by my editors. So, you get to read it here instead.)
Pulsars are rapidly-spinning neutron stars, the very small dense remnants of stars at least 8 times more massive than the Sun. Their pulses are intense beams of light that sweep across our field of view each time the neutron star rotates. A pulsar’s rotation slows down over time, though, and some researchers in the UK have proposed a simple physical model that refines the most widely accepted theory.
Observations of the matter expelled by the initial supernova can be used to estimate the age of the pulsar; those numbers can be compared to age estimates based on its spin slowdown. In some cases, these estimates match reasonably well, but in others, they give wildly different results, differing by thousands of years at the extreme. The researchers’ model began with a different assumption: that the superfluid comprised a higher fraction of the core before things start to cool down. The result is pinning: the vortices in the superfluid stick to one spot relative to each other. That means the superfluid’s rotation rate remains the same, while the rest of the pulsar continues to slow down. [Read more….]