Trigger-Happy Star Formation
This composite image, created using data from the Chandra X-ray Observatory and the Spitzer Space Telescope, shows the molecular cloud Cepheus B, located in our galaxy about 2,400 light years from the Earth. The Spitzer data, in red, green and blue shows the molecular cloud (in the bottom part of the image) plus young stars in and around Cepheus B, and the Chandra data in violet shows the young stars in the field.
The Chandra observations allowed the astronomers to pick out young stars within and near Cepheus B, identified by their strong X-ray emission. The Spitzer data showed whether the young stars have a so-called "protoplanetary" disk around them. Such disks only exist in very young systems where planets are still forming, so their presence is an indication of the age of a star system.
These data provide an excellent opportunity to test a model for how stars form. The new study suggests that star formation in Cepheus B is mainly triggered by radiation from one bright, massive star (HD 217086) outside the molecular cloud. According to the particular model of triggered star formation that was tested — called the radiation-driven implosion (RDI) model — radiation from this massive star drives a compression wave into the cloud triggering star formation in the interior, while evaporating the cloud’s outer layers.
Different types of triggered star formation have been observed in other environments. For example, the formation of our solar system was thought to have been triggered by a supernova explosion, In the star-forming region W5, a “collect-and-collapse” mechanism is thought to apply, where shock fronts generated by massive stars sweep up material as they progress outwards.
Eventually the accumulated gas becomes dense enough to collapse and form hundreds of stars. The RDI mechanism is also thought to be responsible for the formation of dozens of stars in W5. The main cause of star formation that does not involve triggering is where a cloud of gas cools, gravity gets the upper hand, and the cloud falls in on itself.
One of the Most Massive Stellar Eruptions Ever Seen in Space
The Pistol Nebula, one of the brightest stars in our galaxy, appears as the bright white dot in the center of this image taken with the Hubble Space Telescope. The image also shows one of the most massive stellar eruptions ever seen in space.
The radiant star has enough raw power to blow off two expanding shells (magenta) of gas equal to the mass of several of our suns. The largest shell is so big (4 light-years) it would stretch nearly all the way from our sun to the next nearest star. The outbursts seen by Hubble are estimated to be only 4,000 and 6,000 years old, respectively.
Despite such a tremendous mass loss, astronomers estimate the extraordinary star presently may be 100 times more massive than our Sun, and may have started with as much as 200 solar masses of material, but it is violently shedding much of its mass.
The star is 25,000 light-years away in the direction of the constellation Sagittarius. Despite its great distance, the star would be visible to the naked eye as a modest 4th magnitude object if it were not for the dust between it and the Earth.
Hubble’s Near Infrared Camera and Multi-Object Spectrometer (NICMOS) was needed to take the picture, because the star is hidden at the galactic center, behind obscuring dust. NICMOS’ infrared vision penetrated the dust to reveal the star, which is glowing with the radiance of 10 million suns.
NGC 281: Living the High Life
High-mass stars are important because they are responsible for much of the energy pumped into our galaxy over its lifetime. Unfortunately, these stars are poorly understood because they are often found relatively far away and can be obscured by gas and dust.
The star cluster NGC 281 is an exception to this rule. It is located about 9,200 light years from Earth and, remarkably, almost 1,000 light years above the plane of the Galaxy, giving astronomers a nearly unfettered view of the star formation within it.
This composite image of NGC 281 contains X-ray data from Chandra (purple) with infrared observations from Spitzer (red, green, blue). The high-mass stars in NGC 281 drive many aspects of their galactic environment through powerful winds flowing from their surfaces and intense radiation that heats surrounding gas, “boiling it away” into interstellar space.
This process results in the formation of large columns of gas and dust, as seen on the left side of the image. These structures likely contain newly forming stars. The eventual deaths of massive stars as supernovas will also seed the galaxy with material and energy.
NGC 281 is known informally as the “Pacman Nebula” because of its appearance in optical images. In optical images the “mouth” of the Pacman character appears dark because of obscuration by dust and gas, but in the infrared Spitzer image the dust in this region glows brightly.
Feast your Eyes on the Fried Egg Nebula
Astronomers have used ESO’s Very Large Telescope to image a colossal star that belongs to one of the rarest classes of stars in the Universe, the yellow hypergiants. The new picture is the best ever taken of a star in this class and shows for the first time a huge dusty double shell surrounding the central hypergiant. The star and its shells resemble an egg white around a yolky centre, leading the astronomers to nickname the object the Fried Egg Nebula.
The monster star, known to astronomers as IRAS 17163-3907, has a diameter about a thousand times bigger than our Sun. At a distance of about 13,000 light-years from Earth, it is the closest yellow hypergiant found to date and new observations show it shines some 500,000 times more brightly than the Sun.
If the Fried Egg Nebula were placed in the centre of the Solar System the Earth would lie deep within the star itself and the planet Jupiter would be orbiting just above its surface. The much larger surrounding nebula would engulf all the planets and dwarf planets and even some of the comets that orbit far beyond the orbit of Neptune. The outer shell has a radius of 10,000 times the distance from the Earth to the Sun.
Yellow hypergiants are in an extremely active phase of their evolution, undergoing a series of explosive events — this star has ejected four times the mass of the Sun in just a few hundred years. The material flung out during these bursts has formed the extensive double shell of the nebula, which is made of dust rich in silicates and mixed with gas.
This activity also shows that the star is likely to soon die an explosive death — it will be one of the next supernova explosions in our galaxy.
Asteroid caught marching across Tadpole Nebula
This infrared image from the WISE telescope showcases the Tadpole Nebula, a star-forming hub in the Auriga constellation about 12,000 light-years from Earth. As WISE scanned the sky it happened to catch an asteroid in our solar system passing by. The asteroid, called 1719 Jens, left tracks across the image. A second asteroid was also observed cruising by.
But that’s not all that WISE caught in this busy image — two natural satellites orbiting above WISE streak through the image, appearing as faint green trails. This Tadpole region is chock full of stars as young as only a million years old and masses over 10 times that of our sun.
It is called the Tadpole nebula because the masses of hot, young stars are blasting out ultraviolet radiation that has etched the gas into two tadpole-shaped pillars, called Sim 129 and Sim 130. These “tadpoles” appear as the yellow squiggles near the center of the frame. The knotted regions at their heads are likely to contain new young stars.
The Pencil Nebula Supernova Shockwave
At 500,000 kilometers per hour, a supernova shockwave plows through interstellar space. This shockwave is known as the Pencil Nebula, or NGC 2736, and is part of the Vela supernova remnant, an expanding shell of a star that exploded about 11,000 years ago.
Initially the shockwave was moving at millions of kilometers per hour, but the weight of all the gas it has swept up has slowed it considerably. Pictured above, the shockwave moves from left to right, as can be discerned by the lack of gas on the left. The above region spans nearly a light year across, a small part of the 100+ light-year span of the entire Vela supernova remnant.
An Angry Bird in the Sky
A new image from the Wide Field Imager on the MPG/ESO 2.2-metre telescope reveals the Lambda Centauri Nebula, a cloud of glowing hydrogen and newborn stars in the constellation of Centaurus. The nebula, also known as IC 2944, is sometimes nicknamed the Running Chicken Nebula, from a bird-like shape some people see in its brightest region, though there is some disagreement over exactly which part of the nebula is chicken shaped, with various bird-like features in evidence across the picture.
In the nebula, which lies around 6500 light-years from Earth, hot newborn stars that formed from clouds of hydrogen gas shine brightly with ultraviolet light. This intense radiation in turn excites the surrounding hydrogen cloud, making it glow a distinctive shade of red, typical of star-forming regions.
The series of opaque black clumps silhouetted against the red background are examples of a type of object called Bok globules. They appear dark as they absorb the light from the luminous background. However, observations of these dark clouds using infrared telescopes have revealed that stars are forming within many of them.
These glowing nebulae are relatively short-lived in astronomical terms (typically a few million years), meaning that the Lambda Centauri Nebula will eventually fade away as it loses both its gas and its supply of ultraviolet radiation.
Vela Supernova Remnant
The Vela supernova remnant is a supernova remnant in the southern constellation Vela, one of the closest known to us. Its source supernova exploded approximately 11,000-12,300 years ago (and was about 800 light years away).
The Vela supernova remnant includes NGC 2736. It also overlaps the Puppis Supernova Remnant, which is four times more distant. Both the Puppis and Vela remnants are among the largest and brightest features in the x-ray sky.
Fighting Dragons of Ara (NGC 6188 & 6164)
NGC 6188 is an emission nebula located about 4,000 light years away in the constellation Ara. The bright open cluster NGC 6193, visible to the naked eye, is responsible for a region of reflection nebulosity within NGC 6188.
Into the Depths of the Lagoon Nebula
Swirling dust clouds and bright newborn stars dominate the view in this image of the Lagoon nebula from NASA’s Spitzer Space Telescope. Also known as Messier 8 and NGC 6523, astronomers estimate it to be between 4000 and 6000 light years away, lying in the general direction of the center of our galaxy in the constellation Sagittarius.
The glowing waters of the Lagoon, as seen in visible light, are really pools of hot gas surrounding the massive, young stars found here. Spitzers infrared vision looks past the gas to show the dusty basin that it fills. Here we see the central regions of the Lagoon with green showing the glow of carbon-based dust grains, and red highlighting the thermal glow of the hottest dust.
The various columns of dust all seem to point inwards towards the central depths of the Lagoon. These structures are being sculpted by the intense glow of giant, young stars found at the nebulas core. Within these clouds of dust and gas, a new generation of stars is forming.
The Elephant Trunk Nebula
Resembling a creature on the run with flames streaming behind it, the Elephant Trunk Nebula is one of few large nebulas that can be seen with the naked eye, although only under extremely dark skies. The nebula is located in the constellation of Cepheus, approximately 2,400 light years away.
This image was taken by Bob and Janice Fera taken between July 23-26, 2011 from Eagle Ridge Observatory, Foresthill, CA.
The elephant trunk nebula is an emission nebula, which means it has a cloud of ionized gas emitting light of various colors, typically through high-energy photons. Scientists believe the nebula could be a site for star formation with young stars emerging from a small cavity in the head of the globule.
A Starfish in the Sky
In the Aquila constellation lies a star nearing the end of its life that is surrounded by a starfish-shaped cloud of gas and dust. A striking image of this object, known as IRAS 19024+0044 has been captured by the Hubble Space Telescope. Protoplanetary nebulae offer glimpses of how stars similar to the Sun end their lives and how they make the transition to white dwarfs surrounded by planetary nebulae.
Clearly visible in this image are five blue lobes that extend away from the central star and give the nebula its asymmetric starfish shape. While astronomers have come up with theories for the origin of these structures, such as direction-changing jets or explosive ejections of matter from the star, their formation is not entirely understood.
The Beauty of Asymmetry
Planetary nebulae signal the demise of mid-sized stars (up to about eight times the mass of the Sun); when the star’s hydrogen fuel supply is exhausted, its outer layers expand and cool, creating a cocoon of gas and dust. This gas then glows as it is bathed in the strong ultraviolet radiation from the central star. NGC 5882 is a quite bright, but small, example of a planetary nebula that lies deep in the southern Milky Way in the constellation of Lupus.
Planetary nebulae sometimes have a perfectly symmetrical appearance, with gas being bellowed out from the dying star evenly in every direction. However, this isn’t the case for NGC 5882. It appears to have two distinct, but non-uniform regions: an elongated inner shell of gas and a fainter aspherical shell that surrounds it.
Hubble’s sharp view reveals the intricate knots, filaments and bubbles within these shells. But it’s the dying star at the heart of the planetary nebula that dominates the image, shining brightly with an incredible surface temperature of about 70,000 °Celsius. (For comparison, the surface temperature of the Sun is only about 5500 °Celsius.) The high surface temperature of this white dwarf is a result of the star’s struggle for survival, finding new ways to prevent itself from collapsing under its own gravity.
A rich collection of colorful astronomical objects is revealed in this picturesque image of the Rho Ophiuchi cloud complex, which is found rising above the plane of the Milky Way in the night sky, bordering the constellations Ophiuchus and Scorpius. It’s one of the nearest star-forming regions to Earth.
The amazing variety of different colors seen in this image represents different wavelengths of infrared light. The bright white nebula in the center of the image is glowing due to heating from nearby stars, resulting in what is called an emission nebula. The same is true for most of the multi-hued gas prevalent throughout the entire image, including the bluish bow-shaped feature near the bottom right. The bright red area in the bottom right is light from the star in the center – Sigma Scorpii – that is reflected off of the dust surrounding it, creating what is called a reflection nebula. And the much darker areas scattered throughout the image are pockets of cool dense gas that block out the background light, resulting in absorption (or ‘dark’) nebulae.
The bright pink objects just left of center are baby stars just now forming; many of them are still enveloped in their own tiny compact nebulae. Some of the oldest stars in our Milky Way Galaxy are also visible in this image, found in two separate (and much more distant) globular clusters: M80 at the far right edge of the image towards the top, and NGC 6144, close to the bottom edge near the center.
The Rose-red Glow of Star Formation
The vivid red cloud in this new image from ESO’s Very Large Telescope is a region of ionised hydrogen surrounding the star cluster NGC 371. This stellar nursery lies in our neighbouring galaxy, the Small Magellanic Cloud.
NGC 371 is a HII region; it is an open cluster surrounded by a nebula. The stars in open clusters all originate from the same diffuse HII region, and over time the majority of the hydrogen is used up by star formation, leaving behind a shell of hydrogen such as the one in this image, along with a cluster of hot young stars. These energetic youngsters emit copious amounts of ultraviolet radiation causing surrounding gas to light up with a colourful glow that extends for hundreds of light-years in every direction.
NGC 371 is of particular interest due to the unexpectedly large number of variable stars it contains. These are stars that change in brightness over time. A particularly interesting type of variable star, known as slowly pulsating B stars, can also be used to study the interior of stars through asteroseismology, and several of these have been confirmed in this cluster. Variable stars play a pivotal role in astronomy: some types are invaluable for determining distances to far-off galaxies and the age of the Universe.