Astronomers using the National Science Foundation’s Very Large Array (VLA) have found a long-sought “missing link” between supernova explosions that generate gamma-ray bursts (GRBs) and those that don’t. The scientists found that a stellar explosion seen in 2012 has many characteristics expected of one that generates a powerful burst of gamma rays, yet no such burst occurred.
“This is a striking result that provides a key insight about the mechanism underlying these explosions,” said Sayan Chakraborti, of the Harvard-Smithsonian Center for Astrophysics (CfA). “This object fills in a gap between GRBs and other supernovae of this type, showing us that a wide range of activity is possible in such blasts,” he added.
The object, called Supernova 2012ap (SN 2012ap) is what astronomers term a core-collapse supernova. This type of blast occurs when the nuclear fusion reactions at the core of a very massive star no longer can provide the energy needed to hold up the core against the weight of the outer parts of the star. The core then collapses catastrophically into a superdense neutron star or a black hole. The rest of the star’s material is blasted into space in a supernova explosion.
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After spending more than a month in orbit on the dark side of dwarf planet Ceres, NASA’s Dawn spacecraft has captured several views of the sunlit north pole of this intriguing world. These images were taken on April 10 from a distance of 21,000 miles (33,000 kilometers), and they represent the highest-resolution views of Ceres to date.
Subsequent images of Ceres will show surface features at increasingly better resolution.
Dawn arrived at Ceres on March 6, marking the first time a spacecraft has orbited a dwarf planet. Previously, the spacecraft explored giant asteroid Vesta for 14 months from 2011 to 2012. Dawn has the distinction of being the only spacecraft to orbit two extraterrestrial targets.
Astronomers have discovered that the winds from supermassive black holes at the centre of galaxies blow outward in all directions, a suspected phenomenon that had been difficult to prove before now.
These new findings, by an international team of astrophysicists, were made possible by simultaneous observations of the luminous quasar PDS 456 with ESA’s XMM-Newton and NASA’s NuSTAR X-ray telescopes, and support the picture of black holes having a significant impact on star formation in their host galaxies.
At the core of every massive galaxy in the Universe, including our own Milky Way, sits a supermassive black hole, with a mass some millions or billions of times that of our Sun. Some of these black holes are active, meaning that their intense gravitational pull causes matter to spiral inward, and at the same time part of that matter is cast away through powerful winds.
The magnetic field that covers the Sun and determines its behavior –the eleven year cycles no less than such conspicuous phenomena as solar spots and solar storms– also has another side to it: a magnetic web that covers the entire surface of the Sun at rest and whose net magnetic flow is greater than that of the active areas. A study led by the Institute of Astrophysics of Andalusia (IAA-CSIC) has revealed where the flow that feeds this web comes from.
The outline of the solar magnetic web coincides with the boundaries of the so-called supergranules, structures linked to the existence of hot gas rising to the surface (similar to the bubbles made by boiling water) some twenty thousand kilometers in diameter.
“We have discovered that inside these supergranules, in what is known as intranetwork, small magnetic elements appear which travel toward the outer boundaries and interact with the web”, says Milan Gosic, IAA researcher in charge of the study.
NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) and ESA’s (European Space Agency) XMM-Newton telescope are showing that fierce winds from a supermassive black hole blow outward in all directions — a phenomenon that had been suspected, but difficult to prove until now.
This discovery has given astronomers their first opportunity to measure the strength of these ultra-fast winds and prove they are powerful enough to inhibit the host galaxy’s ability to make new stars
“We know black holes in the centers of galaxies can feed on matter, and this process can produce winds. This is thought to regulate the growth of the galaxies,” said Fiona Harrison of the California Institute of Technology (Caltech) in Pasadena, California. Harrison is the principal investigator of NuSTAR and a co-author on a new paper about these results appearing in the journal Science. “Knowing the speed, shape and size of the winds, we can now figure out how powerful they are.”
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Astronomers have used NASA’s Hubble Space Telescope to take the most detailed picture to date of a large, edge-on, gas-and-dust disk encircling the 20-million-year-old star Beta Pictoris.
Beta Pictoris remains the only directly imaged debris disk that has a giant planet (discovered in 2009). Because the orbital period is comparatively short (estimated to be between 18 and 22 years), astronomers can see large motion in just a few years. This allows scientists to study how the Beta Pictoris disk is distorted by the presence of a massive planet embedded within the disk.
The new visible-light Hubble image traces the disk in closer to the star to within about 650 million miles of the star (which is inside the radius of Saturn’s orbit about the Sun).
“Some computer simulations predicted a complicated structure for the inner disk due to the gravitational pull by the short-period giant planet. The new images reveal the inner disk and confirm the predicted structures. This finding validates models, which will help us to deduce the presence of other exoplanets in other disks,” said Daniel Apai of the University of Arizona. The gas-giant planet in the Beta Pictoris system was directly imaged in infrared light by the European Southern Observatory’s Very Large Telescope six years ago.
As the sun skims through the galaxy, it flings out charged particles in a stream of plasma called the solar wind, and the solar wind creates a bubble extending far outside the solar system known as the heliosphere. For decades, scientists have visualized the heliosphere as shaped like a comet, with a very long tail extending thousands of times as far as the distance from the Earth to the sun.
New research suggests that the sun’s magnetic field controls the large-scale shape of the heliosphere “much more than had been previously thought,” says Merav Opher, associate professor of astronomy and director of the Center for Space Physics at Boston University (BU). In the new model, the magnetic field squeezes the solar wind along the sun’s North and South axes, producing two jets that are then dragged downstream by the flow of the interstellar medium through which the heliosphere moves.