October 13, 2017

Smoke from California wildfires seen by Sentinel-3A satellite

Smoke over California seen by Sentinel-3A satellite

The Copernicus Sentinel-3A satellite captured this image of smoke from wildfires in the US state of California on 9 October 2017.

Wildfires broke out in parts of the state on 8 October 2017 around Napa Valley, and the smoke was spread by strong northeasterly winds.

Image Credit: ESA

Supernova Remnant G292.0+1.8

Supernova Remnant G292.0+1.8

At a distance of about 20,000 light years, G292.0+1.8 is one of only three supernova remnants in the Milky Way known to contain large amounts of oxygen. These oxygen-rich supernovas are of great interest to astronomers because they are one of the primary sources of the heavy elements (that is, everything other than hydrogen and helium) necessary to form planets and people. The X-ray image from Chandra shows a rapidly expanding, intricately structured, debris field that contains, along with oxygen (yellow and orange), other elements such as magnesium (green) and silicon and sulfur (blue) that were forged in the star before it exploded.

Image Credit: NASA/CXC/SAO
Explanation from: https://www.nasa.gov/chandra/multimedia/chandra-15th-anniversary-g292.html

Dual Supermassive Black Holes

Dual Supermassive Black Holes
This illustration depicts two centrally located supermassive black holes surrounded by disks of hot gas. The black holes orbit each other for hundreds of millions of years before they merge to form a single supermassive black hole that sends out intense gravitational waves.

  • Five new pairs of merging supermassive black holes have been discovered by combining data from different telescopes.
  • Models predict such growing dual supermassive black holes, but relatively few have been found.
  • Researchers used Chandra observations to follow up on promising candidate mergers identified in optical and infrared studies.
  • X-ray and infrared radiation is able to penetrate obscuring clouds of gas and dust that keep these black hole pairs otherwise hidden.

This graphic shows two of five new pairs of supermassive black holes recently identified by astronomers using a combination of data from NASA's Chandra X-ray Observatory, the Wide-Field Infrared Survey Explorer (WISE), the ground-based Large Binocular Telescope in Arizona, and the Sloan Digital Sky Survey (SDSS) Mapping Nearby Galaxies at APO (MaNGA) survey. This discovery could help astronomers better understand how giant black holes grow and how they may produce the strongest gravitational wave signals in the Universe.

Each pair contains two supermassive black holes weighing millions of times the mass of the Sun. These black hole couples formed when two galaxies collided and merged with each other, forcing their supermassive black holes close together. While theoretical models have predicted such giant growing black hole pairings should be relatively abundant, they have been difficult to find.

To uncover these latest supermassive black hole pairs, astronomers used optical data from the Sloan Digital Sky Survey (SDSS) — shown in the main panel of each image — to identify galaxies where it appeared that a merger between two smaller galaxies was underway. Next, they selected objects where the separation between the centers of the two galaxies in the SDSS data is less than 30,000 light years, and the infrared colors from WISE data match those predicted for a rapidly growing supermassive black hole.

Seven merging systems containing at least one supermassive black hole were found with this technique. Because strong X-ray emission is a hallmark of growing supermassive black holes, the team then observed these systems with Chandra. They found that five systems contained pairs of X-ray sources that were separated by a relatively small distance (see inset for two examples), providing compelling evidence that they contain two growing, or feeding, supermassive black holes.

Both the X-ray data from Chandra and the infrared WISE observations suggest that the supermassive black holes are buried in large amounts of dust and gas. Because these two wavelengths are able to penetrate the obscuring clouds, this makes the combination of infrared selection with X-ray follow-up a very effective way to find these black hole pairs. Chandra's sharp vision is also critical as it is able to resolve each of the X-ray sources in the pairs.

Image Credit: NASA/CXC/A.Hobart
Explanation from: http://chandra.harvard.edu/photo/2017/doubleagn/

October 9, 2017

Emission Nebula NGC 6357

Emission Nebula NGC 6357

This image, captured by ESO’s Very Large Telescope (VLT) at Paranal, shows a small part of the well-known emission nebula, NGC 6357, located some 8000 light-years away, in the tail of the southern constellation of Scorpius (The Scorpion). The image glows with the characteristic red of an H II region, and contains a large amount of ionised and excited hydrogen gas.

The cloud is bathed in intense ultraviolet radiation — mainly from the open star cluster Pismis 24, home to some massive, young, blue stars — which it re-emits as visible light, in this distinctive red hue.

The cluster itself is out of the field of view of this picture, its diffuse light seen illuminating the cloud on the centre-right of the image. We are looking at a close-up of the surrounding nebula, showing a mesh of gas, dark dust, and newly born and still forming stars.

Image Credit: ESO
Explanation from: https://www.eso.org/public/images/potw1334a/

Dwarf Galaxy ESO 553-46

Dwarf Galaxy ESO 553-46

As far as galaxies are concerned, size can be deceptive. Some of the largest galaxies in the Universe are dormant, while some dwarf galaxies, such as ESO 553-46 imaged here by the NASA/ESA Hubble Space Telescope, can produce stars at a hair-raising rate. In fact, ESO 553-46 has one of the highest rates of star formation of the 1000 or so galaxies nearest to the Milky Way. No mean feat for such a diminutive galaxy!

Clusters of young, hot stars are speckling the galaxy, burning with a fierce blue glow. The intense radiation they produce also causes surrounding gas to light up, which is bright red in this image. The small mass and distinctive colouring of galaxies of this type prompted astronomers to classify them, appropriately, as blue compact dwarfs (BCD).

Lacking the clear core and structure that many larger galaxies — such as the Milky Way — have, BCDs such as ESO 553-46 are composed of many large clusters of stars bound together by gravity. Their chemical makeup is interesting to astronomers, since they contain relatively little dust and few elements heavier than helium, which are produced in stars and distributed via supernova explosions. Such conditions are strikingly similar to those that existed in the early Universe, when the first galaxies were beginning to form.

Image Credit: ESA/Hubble & NASA
Explanation from: https://www.spacetelescope.org/images/potw1741a/

Dusty Ring around Boyajians Star

Dusty Ring around Boyajians Star

This illustration depicts a hypothetical uneven ring of dust orbitingKIC 8462852, also known as Boyajians Star or Tabby's Star. Astronomers have found the dimming of the star over long periods appears to be weaker at longer infrared wavelengths of light and stronger at shorter ultraviolet wavelengths. Such reddening is characteristic of dust particles and inconsistent with more fanciful alien megastructure concepts, which would evenly dim all wavelengths of light.

By studying observations from NASAsSpitzer and Swift telescopes, as well as the Belgian AstroLAB IRIS observatory, the researchers have been able to better constrain the size of the dust particles. This places them within the range found in dust disks orbiting stars, and larger than the particles typically found in interstellar dust.

The system is portrayed with a couple of comets, consistent with previous studies that have found evidence for cometary activity within the system.

Image Credit: NASA/JPL-Caltech/R. Hurt (IPAC)
Explanation from: http://www.spitzer.caltech.edu/images/6404-ssc2017-11a-Dusty-Ring-Around-Boyajians-Star