An image captured by NASA’s NuSTAR telescope, designed to investigate black holes, is the best-ever view of the sun in high-energy X-ray light.
For the first time, a mission designed to set its eyes on black holes and other objects far from our solar system has turned its gaze back closer to home, capturing images of our sun. NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has taken its first picture of the sun, producing the most sensitive solar portrait ever taken in high-energy X-rays.
“NuSTAR will give us a unique look at the sun, from the deepest to the highest parts of its atmosphere,” said David Smith, a solar physicist and member of the NuSTAR team at University of California, Santa Cruz.
Solar scientists first thought of using NuSTAR to study the sun about seven years ago, after the space telescope’s design and construction was already underway (the telescope launched into space in 2012). Smith had contacted the principal investigator, Fiona Harrison of the California Institute of Technology in Pasadena, who mulled it over and became excited by the idea.
“At first I thought the whole idea was crazy,” says Harrison. “Why would we have the most sensitive high energy X-ray telescope ever built, designed to peer deep into the universe, look at something in our own back yard?” Smith eventually convinced Harrison, explaining that faint X-ray flashes predicted by theorists could only be seen by NuSTAR.
While the sun is too bright for other telescopes such as NASA’s Chandra X-ray Observatory, NuSTAR can safely look at it without the risk of damaging its detectors. The sun is not as bright in the higher-energy X-rays detected by NuSTAR, a factor that depends on the temperature of the sun’s atmosphere.
This first solar image from NuSTAR demonstrates that the telescope can in fact gather data about sun. And it gives insight into questions about the remarkably high temperatures that are found above sunspots — cool, dark patches on the sun. Future images will provide even better data as the sun winds down in its solar cycle.
“We will come into our own when the sun gets quiet,” said Smith, explaining that the sun’s activity will dwindle over the next few years.
With NuSTAR’s high-energy views, it has the potential to capture hypothesized nanoflares — smaller versions of the sun’s giant flares that erupt with charged particles and high-energy radiation. Nanoflares, should they exist, may explain why the sun’s outer atmosphere, called the corona, is sizzling hot, a mystery called the “coronal heating problem.” The corona is, on average, 1.8 million degrees Fahrenheit (1 million degrees Celsius), while the surface of the sun is relatively cooler at 10,800 Fahrenheit (6,000 degrees Celsius). It is like a flame coming out of an ice cube. Nanoflares, in combination with flares, may be sources of the intense heat.
If NuSTAR can catch nanoflares in action, it may help solve this decades-old puzzle.
“NuSTAR will be exquisitely sensitive to the faintest X-ray activity happening in the solar atmosphere, and that includes possible nanoflares,” said Smith.
What’s more, the X-ray observatory can search for hypothesized dark matter particles called axions. Dark matter is five times more abundant than regular matter in the universe. Everyday matter familiar to us, for example in tables and chairs, planets and stars, is only a sliver of what’s out there. While dark matter has been indirectly detected through its gravitational pull, its composition remains unknown.
It’s a long shot, say scientists, but NuSTAR may be able spot axions, one of the leading candidates for dark matter, should they exist. The axions would appear as a spot of X-rays in the center of the sun.
Meanwhile, as the sun awaits future NuSTAR observations, the telescope is continuing with its galactic pursuits, probing black holes, supernova remnants and other extreme objects beyond our solar system.
Credit: NuStar News at Caltech
Ultra-luminous X-ray sources (ULXs) are point sources in the sky that are so bright in X-rays that each emits more radiation than a million suns emit at all wavelengths. ULXs are rare. Most galaxies (including our own Milky Way) have none, and those galaxies that do host a ULX usually contain only one. ULXs are also mysterious objects. They can’t be normal stars because their huge luminosities should then tear them apart.
Most astronomers think that ULXs are black holes more than about ten solar masses in size (so-called intermediate mass black holes) that are accreting matter onto a surrounding disk and emitting X-rays. Bright X-ray emission is not unusual – the nuclei of galaxies also are bright X-ray emitters – but they are super-massive black holes, while ULXs are neither super-massive nor located in galactic nuclei.
CFA astronomers Stefano Mineo and Andy Goulding and their colleagues used the Chandra X-ray Observatory to search for ULXs in a sample of seventeen luminous infrared galaxies that are exceptionally bright because of their extreme star formation activity. If star formation does signal the presence of ULXs, or even produce them, then these objects should have many. The team discovered fifty-three ULXs (with an uncertainty of about 30% ) among the 139 X-ray sources present in this sample.
They report, however, that this ULX figure is actually ten times smaller than would be expected if ULXs correlated with simple star formation activity. They offer several possible explanations for this deficiency, including a surfeit of elements heavier than helium in these galaxies (these elements can suppress the birth of black holes).
But the most likely scenario, they argue, is that large amounts of gas in these galaxies are present and absorbing X-rays, with the result that many of the ULXs present are not detected. Their conclusion implies that deep X-ray surveys of galaxies must take absorbing gas into account when estimating their internal X-ray properties and how this radiation affects the galaxies’ properties and evolution.
Having studied it during its closest approach to the black hole this summer, UCLA astronomers believe that they have solved the riddle of the object widely known as G2. A team led by Andrea Ghez, professor of physics and astronomy in the UCLA College, determined that G2 is most likely a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust — its movements choreographed by the black hole’s power.
Astronomers had figured that if G2 had been a hydrogen cloud, it could have been torn apart by the black hole, and that the resulting celestial fireworks would have dramatically changed the state of the black hole.
Ghez and her colleagues — who include lead author Gunther Witzel, a UCLA postdoctoral scholar, and Mark Morris and Eric Becklin, both UCLA professors of physics and astronomy — conducted the research at Hawaii’s W.M. Keck Observatory, which houses the world’s two largest optical and infrared telescopes.
Ghez said G2 now is undergoing what she calls a “spaghetti-fication” — a common phenomenon near black holes in which large objects become elongated. At the same time, the gas at G2’s surface is being heated by stars around it, creating an enormous cloud of gas and dust that has shrouded most of the massive star.
“We are seeing phenomena about black holes that you can’t watch anywhere else in the universe,” Ghez added. “We are starting to understand the physics of black holes in a way that has never been possible before.” (Credit:via )ucla
The equations of general relativity are so fiendish that nobody has been able to work out what a collision between two black holes would look like, until now… (PDF)
The difficult part of this work is calculating the trajectory of the photons using the physics of general relativity. These equations are notoriously non-linear, so physicist sometimes simplify them by assuming that a system remains constant in the time it takes for light to pass by. The difficulty with black hole binaries is that this assumption does not hold— these objects orbit so rapidly as they approach each other that space-time warps, even during the time it takes for light to pass by.
Andy Bohn(et al.) at Cornell University in Ithaca, New York, reveals how in-spiraling black hole pairs should distort the light field around them. The team has concluded that from large distances, binaries are more or less indistinguishable from single black holes. Only a relatively close observer would be able to see the fascinating detail that they have simulating or one with very high resolving power.
The first observation of much bigger deflections, such as those produced by black holes or black hole pairs, will be something of a triumph for whoever spots them first.via physics arxiv