gas cloud

Astronomy Photo of the Day: 4/27/15 — NGC 371

Meet NGC 371, a celestial region that lurks approximately 200,000 light-years from Earth in the Small Magellanic Cloud (toward the constellation of Tucana).

Based on its appearance, one might come to the conclusion that NGC 371 is the byproduct of supernovae—explosive events that see high-mass stars get obliterated from the inside out—when it is actually in the process of forming new stars. These stars, which remain young and incredibly energetic, have affected their surroundings in a big way… Mostly with the gas.

You see, as these stars come to fruition, they shed a significant amount of mass via solar winds, the infrared radiation contained therein is known to cause ionization in hydrogen gas clouds—the mechanism that allows them to glow spectacularly.

With NGC 371 specifically, the nebula has plenty of ionization fuel, as it is powered by an open cluster of stars (pictured in the center), But ultimately, star formation activity will be staunched altogether, when the last of the hydrogen is consumed, leaving the nebula a shell of its former self (in a figurative and literal sense).

Additionally, the region is somewhat unusual in the fact that it harbors a large number of variable stars (or objects that periodically dim and brighten over time). According to the ESO, “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.”

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Image Credit: ESO/Manu Mejias


V838 Monocerotis

V838 Monocerotis (V838 Mon) is a red variable star in the constellation Monoceros about 20,000 light years from our Sun. The previously unknown star was observed in early 2002 experiencing a major outburst, and was possibly one of the largest known stars for a short period following the outburst. Originally believed to be a typical nova eruption, it was then realized to be something completely different. The reason for the outburst is still uncertain, but several conjectures have been put forward, including an eruption related to stellar death processes and a merger of a binary star or planets.

The remnant is evolving rapidly. By 2009 its temperature had increased to 3,270K and its luminosity was 15,000 times solar, but its radius had decreased to 380 times that of the sun although the ejecta continues to expand. The opaque ejected dust cloud has completely engulfed the B-type companion.

Credit: NASA

Falling Into a Black Hole

A gas cloud named G2 is about to collide with Sagittarius A*, the supermassive black hole at the center of our galaxy. A simulation shows how the cloud might be stretched and torn apart.

Black holes, the ultradense collapsed objects predicted by Einstein’s theory of general relativity, are often depicted as voracious feeders whose extraordinary gravity acts like a one-way membrane: Everything is sucked in, even light, and virtually nothing leaks out.

Now, for the first time, astronomers may have a chance to watch as a giant black hole consumes a cosmic snack.

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Ripped apart by a black hole

New observations from ESO’s Very Large Telescope show for the first time a gas cloud being ripped apart by the supermassive black hole at the centre of the galaxy. The cloud is now so stretched that its front part has passed the closest point and is travelling away from the black hole at more than 10 million km/h, whilst the tail is still falling towards it.

In 2011 ESO’s Very Large Telescope (VLT) discovered a gas cloud with several times the mass of the Earth accelerating towards the black hole at the centre of the Milky Way. This cloud is now making its closest approach and new VLT observations show that it is being grossly stretched by the black hole’s extreme gravitational field.

As the gas cloud is stretched its light gets harder to see. But by staring at the region close to the black hole for more than 20 hours of total exposure time with the SINFONI instrument on the VLT — the deepest exposure of this region ever with an integral field spectrometer  — the team was able to measure the velocities of different parts of the cloud as it streaks past the central black hole.

The climax of this unique event at the centre of the galaxy is now unfolding and being closely watched by astronomers around the world. This intense observing campaign will provide a wealth of data, not only revealing more about the gas cloud, but also probing the regions close to the black hole that have not been previously studied and the effects of super-strong gravity.

Image credit: ESO/S. Gillessen/MPE/Marc Schartmann

The Cat’s Paw Nebula in Infrared

Infrared view of the Cat’s Paw Nebula (NGC 6334) taken by ESO’s VISTA. NGC 6334 is a vast region of star formation about 5500 light-years from Earth in the constellation of Scorpius. The whole gas cloud is about 50 light-years across. NGC 6334 is one of the most active nurseries of young massive stars in our galaxy, some nearly ten times the mass of our Sun and most born in the last few million years.


The Jellyfish Nebula

The Jellyfish Nebula (also known as IC 443 and Sharpless 248 (Sh2-248)) is a galactic supernova remnant in the constellation Gemini. On the plan of the sky, it is located near the star Eta Geminorum. Its distance is roughly 5,000 light years from Earth. The Jellyfish Nebula may be the remains of a supernova that occurred 3,000+ years ago. The same supernova event likely created the neutron star CXOU J061705.3+222127, the collapsed remnant of the stellar core. The Jellyfish Nebula is one of the best-studied  cases of supernova remnants interacting with surrounding molecular clouds.

Credit: Emil Ivanov, Wikipedia.

Dark Matter Protects Gas Cloud

Like a bullet wrapped in a full metal jacket, a high-velocity hydrogen cloud hurtling toward the Milky Way appears to be encased in a shell of dark matter, according to a new analysis of data from the National Science Foundation’s Robert C. Byrd Green Bank Telescope (GBT). Astronomers believe that without this protective shell, the high-velocity cloud (HVC) known as the Smith Cloud would have disintegrated long ago when it first collided with the disk of our Galaxy.

f confirmed by further observations, a halo of dark matter could mean that the Smith Cloud is actually a failed dwarf galaxy, an object that has all the right stuff to form a true galaxy, just not enough to produce stars.

“The Smith Cloud is really one of a kind. It’s fast, quite extensive, and close enough to study in detail,” said Matthew Nichols with the Sauverny Observatory in Switzerland and principal author on a paper accepted for publication in the Monthly Notices of the Royal Astronomical Society. “It’s also a bit of a mystery; an object like this simply shouldn’t survive a trip through the Milky Way, but all the evidence points to the fact that it did.” Previous studies of the Smith Cloud revealed that it first passed through our Galaxy many millions of years ago. By reexamining and carefully modeling the cloud, astronomers now believe that the Smith Cloud contains and is actually wrapped in a substantial “halo” of dark matter – the gravitationally significant yet invisible stuff that makes up roughly 80 percent of all the matter in the Universe.

“Based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing,” observed Jay Lockman, an astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, and one of the coauthors on the paper. “While a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today.” The Milky Way is swarmed by hundreds of high-velocity clouds, which are made up primarily of hydrogen gas that is too rarefied to form stars in any detectable amount. The only way to observe these objects, therefore, is with exquisitely sensitive radio telescopes like the GBT, which can detect the faint emission of neutral hydrogen. If it were visible with the naked eye, the Smith Cloud would cover almost as much sky as the constellation Orion.

Most high-velocity clouds share a common origin with the Milky Way, either as the leftover building blocks of galaxy formation or as clumps of material launched by supernovas in the disk of the galaxy. A rare few, however, are interlopers from farther off in space with their own distinct pedigree. A halo of dark matter would strengthen the case for the Smith Cloud being one of these rare exceptions. Currently, the Smith Cloud is about 8,000 light-years away from the disk of our Galaxy. It is moving toward the Milky Way at more than 150 miles per second and is predicted to impact again in approximately 30 million years. “If confirmed to have dark matter this would in effect be a failed galaxy,” said Nichols. “Such a discovery would begin to show the lower limit of how small a galaxy could be.” The researchers believe this could also improve our understanding of the Milky Way’s earliest star formation.

Image Credit: NRAO/AUI/NSF



Over the past 25 years, Hubble has made more than 1.2 million observations and generated a staggering 100 terabytes of data. Narrowing down my favorite image is nearly impossible but I’ve managed to highlight a few.

The Eagle Nebula
I’m not sure Hubble has produced a more majestic image than this one of the Eagle Nebula. This image shows the famous “Pillars of Creation” and the nebula’s multi-colored glow of gas clouds, wispy tendrils of dark cosmic dust, and the rust-colored elephants’ trunks of the nebula’s famous pillars. The dust and gas in the pillars is seared by the intense radiation from young stars and eroded by strong winds from massive nearby stars. 

Hubble Ultra Deep Field
Peering back to nearly the beginning of time, this image shakes me at my core and illustrates the unimaginable vastness of the cosmos. This view of nearly 10,000 galaxies is the deepest visible-light image of the cosmos. Called the Hubble Ultra Deep Field, this galaxy-studded view represents a "deep” core sample of the universe, cutting across billions of light-years. The snapshot includes galaxies of various ages, sizes, shapes, and colors. The smallest, reddest galaxies, about 100, may be among the most distant known, existing when the universe was just 800 million years old.

The Antennae
The galaxies — also known as NGC 4038 and NGC 4039 — are locked in a deadly embrace. Once spiral galaxies similar to our own Milky Way, the pair have spent the past few hundred million years sparring with one another. This clash is so violent that stars have been ripped from their host galaxies to form a streaming arc between the two. Clouds of gas are seen in bright pink and red, surrounding the bright flashes of blue star-forming regions — some of which are partially obscured by dark patches of dust. The rate of star formation is so high that the Antennae Galaxies are said to be in a state of starburst, a period in which all of the gas within the galaxies is being used to form stars. This is a preview of what might happen when our Milky Way galaxy collides with the approaching Andromeda galaxy in a few billion years. 

The Tarantula Nebula
About 170,000 light-years away, is a turbulent star-forming region in the Large Magellanic Cloud called the Tarantula Nebula. It is so close to Earth that Hubble can make out individual stars. It is home to many extreme conditions including supernova remnants and the heaviest star ever found, R136a1. The Tarantula Nebula is the most luminous nebula of its type in the local Universe as a result of the raucous stellar breeding ground located at its heart known as 30 Doradus.

Helix Nebula
The Helix Nebula, located 690 light-years from Earth, is a ball of glowing gas expelled from a dying sun-like star. This image is a composite of a photograph taken by Hubble in 2002 and one by a telescope in Chile in 2003. The object is so large that both telescopes were needed to capture a complete view. It resembles a simple doughnut as seen from Earth but new evidence suggests that the Helix consists of two gaseous disks nearly perpendicular to each other.


Bok Globules in the Carina Nebula

A Bok globule nicknamed the “caterpillar” appears in the top image. Its glowing edge indicates that it is being photoionized by the hottest stars in the cluster. It has been hypothesized that stars may form inside such dusty cocoons. The top of the Keyhole Nebula, the most prominent feature embedded inside Carina, is in the bottom image. Another Bok globule is in the foreground.

Credit: NASA/ESA/Hubble/N. Smith (University of California, Berkeley)

Milky Way gas cloud causes multiple images of distant quasar

For the first time, astronomers have seen the image of a distant quasar split into multiple images by the effects of a cloud of ionized gas in our own Milky Way Galaxy. Such events were predicted as early as 1970, but the first evidence for one now has come from the National Science Foundation’s Very Long Baseline Array (VLBA) radio telescope system.

The scientists observed the quasar 2023+335, nearly 3 billion light-years from Earth, as part of a long-term study of ongoing changes in some 300 quasars. When they examined a series of images of 2023+335, they noted dramatic differences. The differences, they said, are caused by the radio waves from the quasar being bent as they pass through the Milky Way gas cloud, which moved through our line of sight to the quasar.

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Gas cloud survives collision with Milky Way

A high-velocity cloud hurtling toward the Milky Way should have disintegrated long ago when it first collided with and passed through our Galaxy. The fact that it’s still intact suggests it’s encased in a shell of dark matter, like a Hobbit wrapped in a mithril coat.

Mapping dark matter — the unseen stuff that makes up more than 80 percent of cosmic matter — near our Galaxy is crucial to fully understanding how the Milky Way assembled over cosmic time.

This firstly requires detailed observations of nearby dwarf galaxies — galaxies each totaling a mass less than 10% of the Milky Way’s 200 to 400 billion stars — because they’re enshrouded in dark matter. More recently, it has been suggested that nearby high velocity clouds of hydrogen gas are encased in dark matter as well. But the effects of their dark matter halos remain unknown.

So Matthew Nichols from the Sauverny Observatory in Switzerland and colleagues set out to observe the Smith Cloud — a high-velocity cloud of hydrogen gas located 8,000 lightyears away in the constellation Aquila — in order to better constrain its dark matter halo. They used the Green Bank Telescope (GBT) in west Virginia in order to detect the faint radio emission of neutral hydrogen.

“The Smith Cloud is really one of a kind. It’s fast, quite extensive, and close enough to study in detail,” said Nichols in a press release.  At its distance the cloud (9,800 lightyears long and 3,300 lightyears wide) covers almost as much sky as the constellation Orion.

“It’s also a bit of a mystery; an object like this simply shouldn’t survive a trip through the Milky Way, but all the evidence points to the fact that it did,” said Nichols. Previous studies of the Smith Cloud revealed that it first passed through our Galaxy many millions of years ago. By reexamining and carefully modeling the cloud, Nichols’ team now believes that it’s actually wrapped in a substantial halo of dark matter.

“Based on the currently predicted orbit, we show that a dark matter free cloud would be unlikely to survive this disk crossing,” said coauthor Jay Lockman from the National Radio Astronomy Observatory. “While a cloud with dark matter easily survives the passage and produces an object that looks like the Smith Cloud today.”

Image credit: NRAO / AUI / NSF

NGC 6240

NGC 6240 is a pair of galaxies merging together located about 400 million light years away towards the constellation Ophiuchus. It is surrounded by a huge cloud of gas, as massive as 10 billion Suns and 300,000 light years across. The cloud likely formed from the gas of both galaxies, agitated by the collision, with additions of elements from supernova explosions, slowly expanding and mixing with cooler gas already present.

The galaxies of NGC 6240 are large spiral galaxies, similar to the Milky Way, and will probably form an elliptical galaxy over the next few million years. Both contain supermassive black holes, which could also merge as they spiral towards each other. The collision has fostered an extended burst of star formation with shorter bursts as well. Some of these new stars were massive enough to collapse into supernovae relatively quickly, adding new elements to the surrounding medium.

Image and information from NASA.

A star-forming filament in Taurus

This image from the APEX telescope, of part of the Taurus Molecular Cloud, shows a sinuous filament of cosmic dust more than ten light-years long. In it, newborn stars are hidden, and dense clouds of gas are on the verge of collapsing to form yet more stars. The cosmic dust grains are so cold that observations at submillimetre wavelengths, such as these made by the LABOCA camera on APEX, are needed to detect their faint glow. This image shows two regions in the cloud: the upper-right part of the filament shown here is Barnard 211, while the lower-left part is Barnard 213.

The submillimetre-wavelength observations from the LABOCA camera on APEX, which reveal the heat glow of the cosmic dust grains, are shown here in orange tones. They are superimposed on a visible-light image of the region, which shows the rich background of stars. The bright star above the filament is φ Tauri.

Credit: ESO/APEX (MPIfR/ESO/OSO)/A. Hacar et al./Digitized Sky Survey 2.

Acknowledgment: Davide De Martin.


For the first time, astronomers will have the chance to watch as a giant black hole consumes a gas cloud.
This gas cloud, with the mass of three earths, has been hurtling toward the center of our Milky Way. It is expected to colide with Sagittarius A, a black hole that lies just 26,000 years from Earth, in March or April.

“This is a rare opportunity to witness spoon-feeding of a black hole,” said Avi Loeb, a theoretical astrophysicist at Harvard. “Will the gas reach the black hole, and if so, how quickly? Will the black hole throw up or spit the gas out in the form of an outflow or a jet?

“The experience is as exciting for astronomers,” he went on, “as it is for parents taking the first photos of their infant eating.”

Below in the simulation the gas cloud G2, is about to colide with Sagittarius A. It shows how the cloud might be stretched and torn apart.