The South African Radio Astronomy Observatory (SARAO) has released today a new MeerKAT telescope image of the centre of our Galaxy, showing radio emission from the region with unprecedented clarity and depth. The international team behind the work is publishing the initial science highlights from this image in The Astrophysical Journal. The article is accompanied by a public release of the data to the worldwide astronomical community for their further scientific exploration.
The new MeerKAT image of the Galactic centre region is shown with the Galactic plane running horizontally across the image. Many new and previously-known radio features are evident, including supernova remnants, compact star-forming regions, and the large population of mysterious radio filaments. The broad feature running vertically through the image is the inner part of the (previously discovered) radio bubbles, spanning 1400 light-years across the centre of the Galaxy. Colours indicate bright radio emission, while fainter emission is shown in greyscale. Credit: I. Heywood, SARAO.
A longstanding mystery about the tiny stars that let loose powerful explosions known as Type Ia supernovae might finally be solved. For brief periods, these cataclysmic blasts can outshine an entire galaxy of billions of stars. Astrophysicists want to understand their origins because they are integral to the evolution of galaxies and the study of dark energy.
Type 1a Supernova A visualization of a computer simulation of a Type Ia supernova. Ejected material (brown) from an exploding white dwarf star crashes into its companion star (blue), yielding an ultraviolet pulse of light streaming from the companion star’s location
Giant stars die a violent death. After a life of several million years, they collapse into themselves and then explode in what is known as a supernova.
Visualizations of the 3D progenitor evolution simulation. The top row displays pseudocolor slices of the 28Si mass fraction (top left), flow speed (top right), total mass fraction of iron group nuclei (bottom right), and specific nuclear energy generation rate (bottom left). The separate panels show different times since the start of the 3D simulation: 20 s (left), 100 s (middle), and 155 s (right). This final time is about 5 s before gravitational core collapse. The bottom row shows volume renderings of the surface where the “iron” mass fraction is 0.95 (left) and of the radial velocity (right) both at 155 s of 3D evolution. Source: Michigan State University
Astronomers from the Niels Bohr Institute have observed a super-bright supernova association with a very unusual long lasting gamma-ray burst. Gamma-ray bursts are in rare cases observed in connection with supernovae, which are the deaths of massive stars and they usually only last a few minutes, but the new burst lasted more than a half an hour. The supernova itself was extremely bright – more than three times as bright as the supernovae previously associated with gamma-ray bursts. The results are published in the scientific journal Nature.
Magnetars are some of the most extreme objects we know in the universe. They are extremely compact objects with masses like the Sun, but with radii of only 10-20 km. At the same time, magnetars are extremely powerful magnetic fields – the strongest magnetic fields we know in the universe. (Artists impression, NASA)
This animation shows a neutron star – the core of a star that exploded in a massive supernova. This particular neutron star is known as a pulsar because it sends out rotating beams of X-rays that sweep past Earth like lighthouse beacons. X-ray telescopes like NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, pick up these beams, registering them as pulses of X-ray light.
What causes a pulsar to pulse? In the case of “accreting pulsars,” the process is set in motion when matter from a companion star falls onto the pulsar. The gravity of the pulsar pulls this material from a surrounding disk, as shown in the animation. The strong magnetic fields surrounding the pulsar funnel the infalling material onto two spots above and below the stellar core. This causes the material to heat up to extreme temperatures and release X-rays. As the star rotates, the two X-ray hot spots behave like a lamp in a lighthouse, sweeping around. Only when the “lamps” are facing Earth will NuSTAR pick up the signal – a pulsing of X-rays.
Observations from ESO’s La Silla and Paranal Observatories in Chile have for the first time demonstrated a link between a very long-lasting burst of gamma rays and an unusually bright supernova explosion. The results show that the supernova was not driven by radioactive decay, as expected, but was instead powered by the decaying super-strong magnetic fields around an exotic object called a magnetar.
This artist’s impression shows a supernova and associated gamma-ray burst driven by a rapidly spinning neutron star with a very strong magnetic field — an exotic object known as a magnetar. Source: ESO
This simulated image depicts the explosive death of a white dwarf as a Type Ia supernova with a stellar companion. When the supernova explodes (dark brown), its ejected material slams into the companion star (light blue). The violent collision produces an ultraviolet pulse, which is emitted from the conical hole carved out by the companion star.
Two new studies confirm that the white dwarfs that explode as Type Ia supernovae can approach death in two different ways.
For many years, astronomers have debated just how the white dwarf maxes out its mass. There are two scenarios: either it siphons gas from a “living” companion star until it just can’t swallow any more (called the single-degenerate model), or it merges with another dead star like itself (the double-degenerate model). The growing sense is that white dwarfs probably die both ways.
Two papers in the May 21st Nature support this suspicion. One reports an ultraviolet pulse from a supernova that, the authors say, is a telltale signal that the white dwarf was stealing material from a companion star. The other study finds no evidence for such a signal from three supernovae.
Supercomputer model predictions say that the deaths of stellar giants are lopsided affairs in which debris and the stars’ cores hurtle off in opposite directions. New observations of a recently exploded star back this up.
While observing the remnant of supernova (SN) 1987A, NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, recently detected the unique energy signature of titanium-44, a radioactive version of titanium that is produced during the early stages of a particular type of star explosion, called a Type II, or core-collapse supernova.
“Titanium-44 is unstable. When it decays and turns into calcium, it emits gamma rays at a specific energy, which NuSTAR can detect,” says Fiona Harrison, the professor of physics at Caltech, and NuSTAR’s principal investigator.
By analyzing direction-dependent frequency changes—or Doppler shifts—of energy from titanium-44, Harrison and her team discovered that most of the material is moving away from NuSTAR. The finding, which appears in Science, is the best proof yet that the mechanism that triggers Type II supernovae is inherently lopsided.
The plot of data from NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR (bottom), amounts to a “smoking gun” of evidence in the mystery of how massive stars explode. The observations indicate that supernovae belonging to a class called Type II or core-collapse blast apart in a lopsided fashion, with the core of the star hurtling in one direction, and the ejected material mostly expanding the other way.
NuSTAR made the most precise measurements yet of a radioactive element, called titanium-44, in the supernova remnant called 1987A. NuSTAR sees high-energy X-rays, as shown here in the plot ranging from 60 to more than 80 kiloelectron volts. The spectral signature of titanium-44 is apparent as the two tall peaks. The white line shows where one would expect to see these spectral signatures if the titanium were not moving. The fact that the spectral peaks have shifted to lower energies indicates that the titanium has “redshifted,” and is moving way from us. This is similar to what happens to a train’s whistle as the train leaves the station. The whistle’s sound shifts to lower frequencies.
NuSTAR’s detection of redshifted titanium reveals that the bulk of material ejected in the 1987A supernova is flying way from us at a velocity of 1.6 million miles per hour (2.6 million kilometers per hour). Had the explosion been spherical in nature, the titanium would have been seen flying uniformly in all directions. This is proof that this explosion occurred in an asymmetrical fashion.
On Earth, we can use our five senses to learn about the world around us, but the primary way that we learn about more remote phenomena is through our perception of light in its various forms, and most light is produced by collisions of atoms with each other or with electrons.
The wavelength of the light produced by collisions depends on the speed of the colliding atoms, and the structure of the atom, which varies from one element to the next. Room-temperature collisions typically produce infrared light, higher speed collisions produce optical and ultraviolet light, and collisions typical of multimillion degree gases produce X-rays.
A supernova remnant contains huge quantities of elements such as oxygen, neon, silicon, sulfur, calcium and iron that were made inside the star and expelled into space. It has been estimated that the Cas A supernova remnant contains enough calcium to make several nonillion (a million trillion trillion) glasses of milk.
Each century, about two massive stars in our own galaxy explode, producing
magnificent supernovae. These stellar explosions send fundamental, uncharged
particles called neutrinos streaming our way and generate ripples called
gravitational waves in the fabric of space-time. Scientists are waiting for
the neutrinos and gravitational waves from about 1,000 supernovae that have
already exploded at distant locations in the Milky Way to reach us. Here on
Earth, large, sensitive neutrino and gravitational-wave detectors have the
ability to detect these respective signals, which will provide information
about what happens in the core of collapsing massive stars just before they
explode.
A small X-ray telescope was boosted into orbit by an air-launched Pegasus XL rocket Wednesday, June 13, 2012, the first step in an ambitious low-cost mission to study supermassive black holes believed to be lurking at the cores of galaxies like Earth's Milky Way and to probe the creation of heavy elements in the cataclysmic death throes of massive stars.
Artist's concept of NuSTAR on orbit. NuSTAR has a 10-m (30') mast that deploys after launch to separate the optics modules (right) from the detectors in the focal plane (left). The spacecraft, which controls NuSTAR's pointings, and the solar panels are with the focal plane. NuSTAR has two identical optics modules in order to increase sensitivity. Credit: NASA/JPL-Caltech
Just over 1,200 years ago, the planet was hit by an extremely intense burst of high-energy radiation of unknown cause, scientists studying tree-ring data have found.
Cryptomeria japonica, also known as Japanese Cedar. 14C measurements in annual rings of Japanese cedar trees from AD 750 to AD 820 demonstrated a rapid increase of about 12‰ in the 14C content from AD 774 to 775, which is about 20 times larger than the change attributed to ordinary solar modulation. Image credit: Corrie Barklimore, Forbes, Australia
Observations with NASA's Chandra X-ray Observatory have provided the first X-ray evidence of a supernova shock wave breaking through a cocoon of gas surrounding the star that exploded. This discovery may help astronomers understand why some supernovas are much more powerful than others.
Composite image (X-ray / Optical) of SN 2010jl. The supernova is the bright object near the top right of the galaxy. Credit: X-ray: NASA/CXC/Royal Military College of Canada/P.Chandra et al; Optical: NASA/STScI
