Born of Flame and Thunder
Even as they are being born, new stars exhibit violent activity. Here a proto star throws out huge jets of gas as it tries to form.
Jets are an active, short-lived phase of star formation, lasting only about 100,000 years. Astronomers don’t know what role jets play in the star-formation process or exactly how the star unleashes them.
The disk material gradually spirals onto the star and escapes as high-velocity jets along the star’s spin axis. The speedy jets may initially be confined to narrow beams by the star’s powerful magnetic field. The jet phase stops when the disk runs out of material, usually a few million years after the star’s birth.
As a giant star nears the end of its days, it begins to throw off huge amounts of matter. It was always thought mass loss in red supergiants was a simple, spherical, and uniform outflow, but recent studies of VY Canis Majoris, shown here in polarized light, show it is very complex. The star is ejecting large amounts of gas at a prodigious rate. During the outbursts, the star loses about 10 times more mass than its normal rate.
Astronomers have studied VY Canis Majoris for more than a century. The star is located 5,000 light-years away. It is 500,000 times brighter and about 30 to 40 times more massive than the Sun. If the Sun were replaced with the bloated VY Canis Majoris, its surface could extend to the orbit of Saturn.
An expanding halo of light surrounds a distant star, named V838 Monocerotis (V838 Mon). The illumination of interstellar dust comes from the red supergiant star at the middle of the image, which gave off a flashbulb-like pulse of light two years ago. V838 Mon is located about 20,000 light-years away from Earth in the direction of the constellation Monoceros, placing the star at the outer edge of our Milky Way galaxy.
The expanding illumination of a dusty cloud around the star has been revealing remarkable structures ever since the star suddenly brightened for several weeks in early 2002. Though Hubble has followed the light echo in several snapshots, this new image shows swirls or eddies in the dusty cloud for the first time. These eddies are probably caused by turbulence in the dust and gas around the star as they slowly expand away. The dust and gas were likely ejected from the star in a previous explosion, similar to the 2002 event, which occurred some tens of thousands of years ago. The surrounding dust remained invisible and unsuspected until suddenly illuminated by the recent explosion.
Four hundred years ago, sky watchers, including the famous astronomer Johannes Kepler, were startled by the sudden appearance of a “new star” in the western sky, rivaling the brilliance of the nearby planets. Now, astronomers using NASA’s three great observatories are unraveling the mysteries of the expanding remains of Kepler’s supernova, the last such object seen to explode in our Milky Way galaxy. The supernova is about 13,000 light-years away.
The combined image unveils a bubble-shaped shroud of gas and dust that is 14 light-years wide and is expanding at more than 4 million miles per hour (2,000 kilometers per second). Observations from each telescope highlight distinct features of the supernova remnant, a fast-moving shell of iron-rich material from the exploded star, surrounded by an expanding shock wave that is sweeping up interstellar gas and dust.
Visible-light images from the Hubble telescope’s Advanced Camera for Surveys reveal where the supernova shock wave is slamming into the densest regions of surrounding gas. The bright glowing knots are dense clumps that form behind the shock wave. As the shock plows into material lost from the progenitor star, instabilities left in its wake cause the swept-up gas to fragment into clumps. The Hubble data also show thin filaments of gas that reveal where the shock wave is encountering lower-density, more uniform interstellar material.
One of the most complex planetary nebulae ever seen, NGC 6543, nicknamed the “Cat’s Eye Nebula.” appears to be a double-star system. The dynamical effects of two stars orbiting one another most easily explains the intricate structures, which are much more complicated than features seen in most planetary nebulae. (The two stars are too close together to be individually resolved by Hubble, and instead, appear as a single point of light at the center of the nebula.)
According to this model, a fast “stellar wind” of gas blown off the central star created the elongated shell of dense, glowing gas. This structure is embedded inside two larger lobes of gas blown off the star at an earlier phase. These lobes are “pinched” by a ring of denser gas, presumably ejected along the orbital plane of the binary companion.
The suspected companion star also might be responsible for a pair of high-speed jets of gas that lie at right angles to this equatorial ring. If the companion were pulling in material from a neighboring star, jets escaping along the companion’s rotation axis could be produced.
These jets would explain several puzzling features along the periphery of the gas lobes. Like a stream of water hitting a sand pile, the jets compress gas ahead of them, creating the “curlicue” features and bright arcs near the outer edge of the lobes. The twin jets are now pointing in different directions than these features. This suggests the jets are wobbling, or precessing, and turning on and off periodically.
Echo of Violence
These are the most recent NASA Hubble Space Telescope views of an unusual phenomenon in space called a light echo. Light from a star that erupted nearly five years ago continues propagating outward through a cloud of dust surrounding the star. The light reflects or “echoes” off the dust and then travels to Earth.
The unusual variable star V838 Monocerotis (V838 Mon) continues to puzzle astronomers. This previously inconspicuous star underwent an outburst early in 2002, during which it temporarily increased in brightness to become 600,000 times more luminous than our Sun. Light from this sudden eruption is illuminating the interstellar dust surrounding the star, producing the most spectacular “light echo” in the history of astronomy.
As light from the eruption propagates outward into the dust, it is scattered by the dust and travels to the Earth. The scattered light has travelled an extra distance in comparison to light that reaches Earth directly from the stellar outburst. Observation of the light echo reveals a new and unique “thin-section” through the interstellar dust around the star. The numerous whorls and eddies in the interstellar dust are particularly noticeable. Possibly they have been produced by the effects of magnetic fields in the space between the stars.
The Hubble observations have been used to determine the distance to V838 Mon, using a technique based on the polarization of the reflected light. Hubble has polarizing filters that only pass light that vibrates at certain angles. This method yields a distance of 20,000 light-years for V838 Mon, suggesting that, during its outburst, V838 Mon was one of the brightest stars in the entire Milky Way. Although the reason for the eruption is still unclear, some astronomers have suggested it might have resulted from the collision of two stars.
R Aquarii is an example of a class of double stars called symbiotic stars. It is speculated that a very old star that has already shed its outer layers to become a white dwarf has been violently reactivated by large quantities of fresh material falling onto it from a very nearby stellar companion. Thus fortified with fresh fuel, the white dwarf experiences an extremely rapid burst of nuclear burning akin to a hydrogen bomb. The energy released powers the ejection of a good part of the outer layers of the star at speeds of up to several hundred thousand kilometers per hour.
R Aquarii is relatively near, at a distance of only 700 light-years.
The Hubble telescope has snapped a view of a stellar demolition zone in our Milky Way Galaxy: A massive star, nearing the end of its life, is tearing apart the shell of surrounding material it blew off 250,000 years ago with its strong stellar wind. The shell of material, dubbed the Crescent Nebula (NGC 6888), surrounds the “hefty,” aging star WR 136, an extremely rare and short-lived class of super-hot stars called a Wolf-Rayet. Hubble’s multicolored picture reveals with unprecedented clarity that the shell of matter is a network of filaments and dense knots, all enshrouded in a thin “skin” of gas [seen in blue]. The skin is glowing because it is being blasted by ultraviolet light from WR 136’s explosion of the central star two years ago. Hubble’s view covers a small region at the northeast tip of the nebula, roughly three light-years across. The entire structure is about 16 light-years wide and 25 light-years long. The bright dot near the center of NGC 6888 is WR 136. The nebula resides in the constellation Cygnus, 4,700 light-years from Earth.
Fifteen unique blue stars crowded together in a star cluster. Why so many blue stars?
The most likely explanation for their existence is that they are the ‘naked cores’ of stars that have been stripped of their outer envelope of gas. This could only have happened if stars were so crowded together in the cluster’s core they can gravitationally pull material from each other.
The image is approximately two light-years across. Most of the blues stars are concentrated within 0.5 light-years of each other.
Hubble’s discovery of such stars lends new weight to the notion that the evolution of a star can be affected in very crowded stellar conditions.
This stellar cannibalism could only take place where stars are so crowded together that chances for close encounters are exceptionally high. The blue stars are interpreted as evidence that the core of the star cluster has contracted to an extremely dense condition called “core collapse.”
M15 (15th object in the Messier Catalog) is located 30,000 light-years away in the constellation Pegasus, and it is visible to the naked eye as a hazy spot 1/3rd the diameter of the full Moon.
Two black holes rush toward each other in a race to death. But they will not destroy each other. Instead, they will merge and become a single supermassive black hole. This image of NGC 6240 contains new X-ray data from Chandra (shown in red, orange, and yellow) that has been combined with an optical image from the Hubble Space Telescope originally released in 2008. The two black holes are a mere 3,000 light years apart. Of course, we are not seeing the black holes themselves because by their nature and definition they cannot be seen. The bright point-like sources in the middle of the image are the result surrounding gases being illuminated by the Hawking radiation generated by the black hole and the x-ray and gamma ray radiation resulting from the gasses and dust spiraling into the black hole.
Scientists think these black holes are in such close proximity because they are spiraling toward each other—a process that began about 30 million years ago. It is estimated that the two black holes will eventually drift together and merge into a larger black hole some tens or hundreds of millions of years from now.
The formation of multiple systems of supermassive black holes should be common in the Universe, since many galaxies undergo collisions and mergers with other galaxies, most of which contain supermassive black holes. It is thought that pairs of massive black holes can explain some of the unusual behavior seen by rapidly growing supermassive black holes, such as the distortion and bending seen in the powerful jets they produce. Also, pairs of massive black holes in the process of merging are expected to be the most powerful sources of gravitational waves in the Universe.
- NASA Hubble Site http://hubblesite.org/newscenter/archive/releases/star/