Archive
Widespread Winds And Feedback From Supermassive Black Holes
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 Origin Of The Magnetic Field Covering The Sun Has Been Discovered
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, ESA Telescopes Give Shape To Furious Black Hole Winds
Image credit: NASA/JPL-Caltech
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.”
Link To Full Story
Link To Another Story
Hubble Gets Best View of A Circumstellar Debris Disk Distorted By A Planet
Credit: NASA, ESA, and D. Apai and G. Schneider (University of Arizona)
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.
A New View Of The Solar System: Astrophysical Jets Driven By The Sun
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.
Researchers Find That Earth’s “Plasmaspheric Hiss” Protects Against A Harmful Radiation Belt
Courtesy of the reasearchers/Haystack Observatory
High above Earth’s atmosphere, electrons whiz past at close to the speed of light. Such ultrarelativistic electrons, which make up the outer band of the Van Allen radiation belt, can streak around the planet in a mere five minutes, bombarding anything in their path. Exposure to such high-energy radiation can wreak havoc on satellite electronics, and pose serious health risks to astronauts.
Now researchers at MIT, the University of Colorado, and elsewhere have found there’s a hard limit to how close ultrarelativistic electrons can get to the Earth. The team found that no matter where these electrons are circling around the planet’s equator, they can get no further than about 11,000 kilometers from the Earth’s surface — despite their intense energy.
What’s keeping this high-energy radiation at bay seems to be neither the Earth’s magnetic field nor long-range radio waves, but rather a phenomenon termed “plasmaspheric hiss” — very low-frequency electromagnetic waves in the Earth’s upper atmosphere that, when played through a speaker, resemble static, or white noise.
Link To Full Story
Link To Another Story
Close Pairing Of Venus And Mars On February 20-21
Credit: Sky & Telescope Diagrame.
Look west in twilight this Friday and Saturday (February 20th and 21st), and an unusual astronomical sight will await you.
Brilliant Venus and faint Mars will be paired remarkably close in the sky. And on Friday evening, the crescent Moon joins them in a tight bunch, a beautiful sight. On Saturday Venus and Mars appear even closer together, with the crescent Moon now looking down on them from above.
When it comes to “eyeball astronomy,” nothing is more satisfying than to see a pair of celestial objects appear close together in the sky, what astronomers call a conjunction. And 2015, notes Sky & Telescope’s longtime contributing editor Fred Schaaf, truly deserves to be called the “Year of the Conjunctions.” In January we watched Venus and Mercury come together in the evening twilight, and now comes a similarly close pairing of Venus and Mars. On Saturday they’ll appear 1/2° apart for viewers in North America. That’s about the width of a pencil held at arm’s length.
Link To Full Story
Astronomers Identify The Closest Known Flyby Of A Star To Our Solar System: A Dim Star That Passed Through The Oort Cloud 70,000 Years Ago
Credit: Michael Osadciw/University of Rochester.
A group of astronomers from the US, Europe, Chile and South Africa have determined that 70,000 years ago a recently discovered dim star is likely to have passed through the solar system’s distant cloud of comets, the Oort Cloud. No other star is known to have ever approached our solar system this close – five times closer than the current closest star, Proxima Centauri.
In a paper published in Astrophysical Journal Letters, lead author Eric Mamajek from the University of Rochester and his collaborators analyzed the velocity and trajectory of a low-mass star system nicknamed “Scholz’s star.”
The star’s trajectory suggests that 70,000 years ago it passed roughly 52,000 astronomical units away (or about 0.8 light years, which equals 8 trillion kilometers, or 5 trillion miles). This is astronomically close; our closest neighbor star Proxima Centauri is 4.2 light years distant. In fact, the astronomers explain in the paper that they are 98% certain that it went through what is known as the “outer Oort Cloud” – a region at the edge of the solar system filled with trillions of comets a mile or more across that are thought to give rise to long-period comets orbiting the Sun after their orbits are perturbed.
CAT Scan Of Nearby Supernova Remnant Reveals Frothy Interio
Image: NASA, ESA, and the Hubble Heritage Team
Cassiopeia A, or Cas A for short, is one of the most well studied supernova remnants in our galaxy. But it still holds major surprises. Harvard-Smithsonian and Dartmouth College astronomers have generated a new 3-D map of its interior using the astronomical equivalent of a CAT scan. They found that the Cas A supernova remnant is composed of a collection of about a half dozen massive cavities – or “bubbles.”
“Our three-dimensional map is a rare look at the insides of an exploded star,” says Dan Milisavljevic of the Harvard-Smithsonian Center for Astrophysics (CfA). This research is being published in the Jan. 30 issue of the journal Science.
About 340 years ago a massive star exploded in the constellation Cassiopeia. As the star blew itself apart, extremely hot and radioactive matter rapidly streamed outward from the star’s core, mixing and churning outer debris. The complex physics behind these explosions is difficult to model, even with state-of-the-art simulations run on some of the world’s most powerful supercomputers. However, by carefully studying relatively young supernova remnants like Cas A, astronomers can investigate various key processes that drive these titanic stellar explosions.
Planck: Gravitational Waves Remain Elusive
Cosmic Microwave Background seen by Planck. Credit: ESA and the Planck Collaboration
Despite earlier reports of a possible detection, a joint analysis of data from ESA’s Planck satellite and the ground-based BICEP2 and Keck Array experiments has found no conclusive evidence of primordial gravitational waves.
The Universe began about 13.8 billion years ago and evolved from an extremely hot, dense and uniform state to the rich and complex cosmos of galaxies, stars and planets we see today.
An extraordinary source of information about the Universe’s history is the Cosmic Microwave Background, or CMB, the legacy of light emitted only 380 000 years after the Big Bang.
ESA’s Planck satellite observed this background across the whole sky with unprecedented accuracy, and a broad variety of new findings about the early Universe has already been revealed over the past two years.
But astronomers are still digging ever deeper in the hope of exploring even further back in time: they are searching for a particular signature of cosmic ‘inflation’ – a very brief accelerated expansion that, according to current theory, the Universe experienced when it was only the tiniest fraction of a second old.
AstroNews 