Nasa's Chandra X-ray Observatory was launched into space aboard the Space Shuttle Columbia 15 years ago. Since its deployment on July 23, 1999, Chandra has revolutionised our understanding of the universe through its X-ray vision.
It's one of Nasa's three "Great Observatories", along with the Hubble Space Telescope and Spitzer Space Telescope, and is designed to detect X-ray emission from hot and energetic regions of the universe.
Chandra has observed objects ranging from the closest planets and comets to the most distant known quasars. It has imaged the remains of exploded stars, or supernova remnants, observed the region around the supermassive black hole at the centre of the Milky Way and discovered black holes across the universe.
It has also made a major advance in the study of dark matter and contributed to research on the nature of dark energy.
To celebrate Chandra's 15th anniversary, four new images of supernova remnants – the Crab Nebula, Tycho, G292.0+1.8, and 3C58 – have been released. These supernova remnants are very hot and energetic, and glow brightly in X-ray light, which allows Chandra to capture them in exquisite detail.
Danish astronomer Tycho Brahe first observed the supernova that bears his name more than four centuries ago. The supernova remnant it created is now a bright source of X-rays. The supersonic expansion of the exploded star produced a shock wave moving outward into the surrounding interstellar gas, and another, reverse shock wave moving back into the expanding stellar debris. This Chandra image of Tycho reveals the dynamics of the explosion in detail. The outer shock has produced a rapidly moving shell of extremely high-energy electrons (blue), and the reverse shock has heated the expanding debris to millions of degrees (red and green). There is evidence from the Chandra data that these shock waves may be responsible for some of the cosmic rays - ultra-energetic particles - that pervade the Galaxy and constantly bombard the Earth. Nasa In 1054 AD, Chinese astronomers and others around the world noticed a new bright object in the sky. This "new star" was, in fact, the supernova explosion that created what is now called the Crab Nebula. At the centre of the nebula is an extremely dense, rapidly rotating neutron star left behind by the explosion. The neutron star, also known as a pulsar, is spewing out a blizzard of high-energy particles, producing the expanding X-ray nebula seen by Chandra. In this new image, lower-energy X-rays from Chandra are red, medium energy X-rays are green, and the highest-energy X-rays are blue. Nasa 3C58 is the remnant of a supernova observed in the year 1181 AD by Chinese and Japanese astronomers. This new Chandra image shows the centre of 3C58, which contains a rapidly spinning neutron star surrounded by a thick ring of X-ray emissions. The pulsar also has produced jets of X-rays blasting away from it to both the left and right, and extending trillions of miles. These jets are responsible for creating the elaborate web of loops and swirls. Nasa 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 supernovae 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 sulphur (blue) that were forged in the star before it exploded. Nasa
The observatory was renamed in honour of the late Indian-American Nobel laureate, Subrahmanyan Chandrasekhar. Known to the world as Chandra (which means "moon" or "luminous" in Sanskrit), he was widely regarded as one of the foremost astrophysicists of the 20th century.
"Chandra continues to be one of the most successful missions that Nasa has ever flown as measured against any metric – cost, schedule, technical success and, most of all, scientific discoveries," said Martin Weisskopf, Chandra Project Scientist at the Marshall Space Flight Centre.
IBTimesUK presents some of Chandra's "greatest hits" from the past 15 years. NGC 6543, better known as the Cat's Eye nebula, is a so-called planetary nebula that represents a phase of stellar evolution that the Sun should experience several billion years from now. When a star begins to run out of fuel, it becomes a red giant. In this phase, a star sheds some of its outer layers, eventually leaving behind a hot core that collapses to form a dense white dwarf star. A fast wind emanating from the hot core rams into the ejected atmosphere and pushes it outward. Chandra's X-ray data shows that its central star is surrounded by a cloud of multi-million-degree gas. Nasa The Antennae galaxies, about 62 million light years from Earth, collided more than 100 million years ago, triggering the formation of millions of stars in clouds of dusts and gas in the galaxies. The most massive of these young stars have already sped through their evolution in a few million years and exploded as supernovas. The X-ray image from Chandra shows huge clouds of hot, interstellar gas that have been injected with rich deposits of elements from supernova explosions. This enriched gas, which includes elements such as oxygen, iron, magnesium and silicon, will be incorporated into new generations of stars and planets. The bright, point-like sources in the image are produced by material falling on to black holes and neutron stars that are remnants of the massive stars. Some of these black holes may have masses that are almost one hundred times that of the Sun. Nasa The Sombrero, also known as M104, is one of the largest galaxies in the nearby Virgo cluster, about 28 million light years from Earth. The Chandra observations show that diffuse X-ray emission extends over 60,000 light years from the centre of the Sombrero. The galaxy itself spans 50,000 light years across. Scientists think this extended X-ray glow may be the result of a wind from the galaxy, primarily being driven by supernovas that have exploded within its bulge and disc. Nasa This image of Centaurus A shows a view of a supermassive black hole's power. Jets and lobes powered by the central black hole in this nearby galaxy can be seen as well as the dust lane in the galaxy and background stars. The X-ray jet in the upper left extends for about 13,000 light years away from the black hole. Nasa The Cartwheel Galaxy is part of a group of galaxies 500 million light years away in the directionof the constellation Sculptor. The ring-shaped rim of the galaxy is the result of a rare and spectacular head-on collision between two galaxies. It was probably a normal spiral structure galaxy similar to the Milky Way before the collision; the spiral structure is beginning to re-emerge, as seen in the faint arms or spokes between the outer ring and the bulls-eye shaped nucleus. Nasa VV 340, also known as Arp 302, provides a textbook example of colliding galaxies in the early stages of their interaction. The edge-on galaxy near the top of the image is VV 340 North and the face-on galaxy at the bottom of the image is VV 340 South. Millions of years later these two spirals will merge - much like the Milky Way and Andromeda will likely do billions of years from now. Nasa This highly distorted supernova remnant may contain the most recent black hole formed in the Milky Way. The remnant, called W49B, is about a thousand years old, as seen from Earth, and is at a distance of about 26,000 light years away. Material near the poles of the doomed rotating star was ejected at a much higher speed than material emanating from its equator. Jets shooting away from the star's poles mainly shaped the supernova explosion and its aftermath. Nasa Stephan's Quintet is a compact group of galaxies discovered about 130 years ago and located about 280 million light years from Earth. The curved, light blue ridge running down the centre of the image shows X-ray data from the Chandra X-ray Observatory. Stephan's Quintet provides a rare opportunity to observe a galaxy group in the process of evolving from an X-ray faint system dominated by spiral galaxies to a more developed system dominated by elliptical galaxies and bright X-ray emission. It shows an additional sign of complex interactions in the past, notably the long tails visible in the optical image. These features were probably caused by one or more passages through the galaxy group by NGC 7317. Nasa The Chinese witnessed a mysterious "guest star" that remained in the sky for eight months in 185 AD. This was a supernova, called RCW 86. In the explosion witnessed nearly 2,000 years ago an otherwise-stable white dwarf, or dead star, was pushed beyond the brink of stability when a companion star dumped material onto it. By blowing a wind prior to exploding, the white dwarf was able to clear out a huge "cavity," a region of very low-density surrounding the system. The explosion into this cavity was able to expand much faster than it otherwise would have. Nasa NGC 2392, or the Eskimo Nebula, is a planetary nebula about 4,200 light years from Earth. Planetary nebulae form when a star uses up all of the hydrogen in its core -- an event our Sun will go through in about five billion years. When this happens, the star begins to cool and expand, increasing its radius by tens to hundreds of times. Eventually, the outer layers of the star are carried away leaving behind a hot core with a surface temperature of about 50,000 degrees Celsius, ejecting its outer layers, creating a complex filamentary shell. Nasa This image of the Pinwheel Galaxy, also known as M101, shows that both young and old stars are evenly distributed along the tightly-wound spiral arms. The Pinwheel Galaxy is in the constellation of Ursa Major (also known as the Big Dipper). It is about 70% larger than our own Milky Way, with a diameter of about 170,000 light years, and is 21 million light years from Earth. This means that the light we're seeing in this image left the Pinwheel Galaxy about 21 million years ago - many millions of years before humans ever walked the Earth. Nasa