Hubble Space Telescope image of a supernova more than 10 billion light-years away. This explosion, known as a white dwarf or type Ia supernova, is the most distant of its kind yet seen.

NASA, ESA, A. Riess (STScI and JHU), and D. Jones and S. Rodney (JHU)

When a white dwarf explodes as a type Ia supernova, its death is so bright that its light can be detected across the Universe. A new observation using the Hubble Space Telescope identified the farthest type Ia supernova yet seen, at a distance of greater than 10 billion light-years. In the tradition of supernova surveys, this event was nicknamed for Woodrow Wilson, 28th President of the United States. The previous record-holder, Supernova Mingus, was about 350 million light-years closer to Earth.

White dwarfs are the remains of stars similar in mass to the Sun. Since such a star would have to live out its entire life to form a white dwarf, there are limits to how early in the Universe's history a type Ia supernova can explode. 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.

Astronomers found this violent event by comparing the light from several separate long exposures of the same patch of the sky, known as CANDELS (the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey). Bright as it was, the distance was so great that Supernova Wilson appeared as an enhancement of the luminosity of its host galaxy. The researchers subtracted the light of the galaxy without the supernova from the combined supernova-galaxy combination, then analyzed the residual light to identify it as type Ia.

Artist's impression of the progenitor system of a type Iax supernova. A massive star dumps gas onto a white dwarf companion, forming a hot accretion disk. The extra mass causes a thermonuclear explosion, which may or may not destroy the white dwarf.

Christine Pulliam (CfA)

Supernovae can be divided into two broad categories: those produced by the deaths of very massive stars, and those that involve the explosions of white dwarfs. Within the first category, supernovae vary greatly depending on a number of details, including the mass of the exploding star. On the other hand, white dwarfs seem to all explode in very similar ways, which is why they have proven useful in measuring distances across the Universe.

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.

In the early days of supernova research, explosions were classified primarily by how much hydrogen and helium they had in their spectra. Type I supernovas, for example, mostly lack both elements. Since stars are mostly composed of hydrogen and helium, that indicates progenitor systems for type I supernovae are unlikely to be exploding stars.

NGC 1365, the Great Barred Spiral Galaxy, in visible light and X-rays (inset). Astronomers determined the strong X-ray emissions from the black hole at the center of this galaxy are due in part to reflection off gas moving nearly at the speed of light.

Optical: SSRO-South, X-ray: NASA/CXC/CfA/INAF/Risaliti

The space near black holes is one of the most extreme environments in the Universe. The bodies' strong gravity and rotation combine to create rapidly spinning disks of matter that can emit huge amounts of light at very high energies. However, the exact mechanism by which this light is produced is uncertain, largely because high-resolution observations of black holes are hard to do. Despite their outsized influence, black holes are physically small: even a black hole a billion times the mass of the Sun occupies less volume than the Solar System.

A new X-ray observation of the region surrounding the supermassive black hole in the Great Barred Spiral Galaxy may have answered one of the big questions. G. Risaliti and colleagues found the distinct signature of X-rays reflecting off gas orbiting the black hole at nearly the speed of light. The detailed information the astronomers gleaned allowed them to rule out some explanations for the bright X-ray emission, bringing us closer to an understanding of the extreme environment near these gravitational engines.

Despite the stereotype of black holes "sucking" matter in, they attract it via gravity. That means stars, gas, and other things can fall into orbits around black holes, which may be stable for long periods of time. Gas often forms accretion disks and jets that release huge amounts of energy in the form of light. This energy can include X-ray emissions. So despite their name, black holes can be very luminous objects.

A Hubble Space Telescope image of the galaxy NGC 4526, overlaid with submillimeter observations (shown here in purple). The submillimeter light shows the presence of molecular gas, which could assist in estimating the mass of the galaxy's central black hole.

NASA/ESA/Timothy A. Davis

The data is good: nearly every large galaxy has at least one supermassive black hole in its nucleus. The data is bad: there generally seems to be a connection between the mass of the black hole and the size of the galaxy's bulge, at least for many galaxies. And the data is ugly: accurate direct measurements of black hole masses are hard to come by, since they're buried deep in the middle of their host galaxies.

A promising technique has used gas dynamics in the galaxy as a black hole mass tracer, as proposed by Timothy A. Davis, Martin Bureau, Michele Cappellari, Marc Sarzi, and Leo Blitz. They tested their hypothesis on a galaxy that has a large amount of carbon monoxide emissions, prime for observations with submillimeter observatories. This method requires far less observation time than many other techniques, meaning that many supermassive black holes could potentially be surveyed.

Measuring supermassive black hole (SMBH) masses is not always straightforward. Astronomers can estimate masses by tracking stars in the central regions of galaxies as they orbit the black hole or by mapping emission by nearby ionized gas. Another promising method used X-ray and radio light for the most massive galaxies in the Universe. But these techniques aren't possible for all galaxies

The star V838 Monocerotis erupted catastrophically in 2002, growing from obscurity to become one of the brightest known stars in the Milky Way. As the comic strip above shows, it shed a lot of mass during the process. A new model may explain how this happened, if the star was actually part of a binary.

NASA/ESA/The Hubble Heritage Team (STScI/AURA)

Stars are plasma, gas ionized as the result of extreme internal temperatures. A solitary star will be mostly spherical under the force of its own gravity. However, when stars are in close binaries, their mutual attraction distorts their shapes. The extreme version of this is the common envelope stage, wherein the stars' outer regions merge to make a single, huge double star. According to theory, that is. While nobody seriously doubts this model, all the observational evidence for common envelope binaries is indirect.

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.

The most famous red transient outburst came from the star euphoniously known as V838 Monocerotis. Before 2002, nobody had noticed the star at all, but for a brief period of time, it expanded hugely, flared brightly, and shed an impressive amount of gas and dust into surrounding space. The Hubble Space Telescope (HST) tracked the outburst over the intervening years, but despite the regular check-ins, there is no widely accepted explanation for it.

Composite X-ray, visible light, and radio image of the bright massive galaxy PKS 0745. Based on X-ray and radio emissions, this black hole could be as much as ten times more massive than previously estimated.

X-ray: NASA/CXC/Stanford/Hlavacek-Larrondo, J. et al; Optical: NASA/STScI; Radio: NSF/NRAO/VLA

Most large galaxies host a supermassive black hole, ranging from millions to billions of times the mass of the Sun. Based on the study of many systems, astronomers discovered a correlation between certain properties of a galaxy and the mass of its central black hole. This relationship seems universal, but we've only been able to examine a subset of the galaxies out there. Black hole masses have only been measured for some of the biggest galaxies in the local Universe—the bright, massive galaxies that sit at the centers of galaxy clusters.

A recent study has used an independent means of estimating black hole masses, based on their brightness in X-rays and radio light. J. Hlavacek-Larrondo, A. C. Fabian, A. C. Edge, and M. T. Hogan examined the massive central galaxies in 18 galaxy clusters and found that previous measurements could be off by as much as a factor of ten. In other words, if the luminosity-based measurements are correct, a black hole currently thought to be 6 billion times the mass of the Sun could actually be 60 billion times more massive than our local star.

That leaves two possibilities: either black holes in bright cluster galaxies behave differently by producing more light than we think they should, or the biggest black holes in the Universe might be astoundingly ultramassive.

An artist's conception of the jets produced by an active galaxy.

NASA

Recently, we discussed the discovery of a black hole in a neighboring galaxy. It appears to be swallowing matter at a rate that's close to the theoretical limit on this process. This discovery raises the hope that we'll be able to get a clear view of the environment around the black hole, where the inflow of matter leads to the formation of particle jets that expel some of the matter at relativistic speeds. This process is also thought to power quasars, where the jets of supermassive black holes generates some of the brightest objects in the Universe.

But there's a small caveat that should temper astronomers' enthusiasm: we don't know for a fact the same process that powers jets from small black holes can scale up to objects that may weigh billions of times the mass of the Sun. Conveniently, in the same week this discovery was announced, another team of astronomers has provided evidence that all of these jets have similar properties.

Although black holes are happy to swallow most of the matter that comes there way, a bit of it escapes—if by "escapes" we mean "gets shot away from the black hole at nearly the speed of light." These jets of particles are so energetic that, in at least some cases, they're entirely thrown out of the galaxy where the black hole resides. Various models indicate the black hole's intense magnetic field lines power the jets by latching on to charged particles in the matter that is falling in towards the event horizon.