Astronomers observe distant galaxy powered by primordial cosmic fuel

Image of a galaxy (center) with incoming cold gas flow, produced by rendering the gas distribution in a supercomputer simulation of a forming galaxy.

A stream of primordial inflowing gas is illuminated from behind by a distant background quasar (lower left; quasar added by an artist, along with the starry background).

Using data collected from the W. M. Keck Observatory, the largest optical telescopes in the world, researchers led by Neil Crighton (MPIA and Swinburne University of Technology) have now made the first unambiguous detection of this accretion of pristine gas onto a star-forming galaxy, that was previously theorized to exist based on cosmological simulations of galaxy formation.

This simulation shown here was run by the Making Galaxies in a Cosmological Context (MaGICC) project in the theory group at MPIA. Credit: MPIA (G. STINSON / A. V. MACCIÒ)

Astronomers have detected cold streams of primordial hydrogen, vestigial matter left over from the Big Bang, fueling a distant star-forming galaxy in the early Universe.

Profuse flows of gas onto galaxies are believed to be crucial for explaining an era 10 billion years ago, when galaxies were copiously forming stars.

To make this discovery, the astronomers – led by Neil Crighton of the Max Planck Institute for Astronomy and Swinburne University – made use of a cosmic coincidence: a bright, distant quasar acting as a "cosmic lighthouse" illuminates the gas flow from behind.

The results were published October 2 in the Astrophysical Journal Letters.

More information: dx.doi.org/10.1088/2041-8205/776/2/L18

ESA's ESO VLT: Observations Identifies Rare "Green Bean" Galaxy

A new galaxy class has been identified using observations from ESO's Very Large Telescope (VLT), the Gemini South telescope, and the Canada-France-Hawaii Telescope (CFHT).

Nicknamed "green bean galaxies" because of their unusual appearance, these galaxies glow in the intense light emitted from the surroundings of monster black holes and are amongst the rarest objects in the Universe.

Read the full Research Paper Here

Many galaxies have a giant black hole at their centre that causes the gas around it to glow. However, in the case of green bean galaxies, the entire galaxy is glowing, not just the centre.

These new observations reveal the largest and brightest glowing regions ever found, thought to be powered by central black holes that were formerly very active but are now switching off.

Astronomer Mischa Schirmer of the Gemini Observatory had looked at many images of the distant Universe, searching for clusters of galaxies, but when he came across one object in an image from the Canada-France-Hawaii Telescope he was stunned -- it looked like a galaxy, but it was bright green.

It was unlike any galaxy he had ever seen before, something totally unexpected. He quickly applied to use ESO's Very Large Telescope to find out what was creating the unusual green glow.

"ESO granted me special observing time at very short notice and just a few days after I submitted my proposal, this bizarre object was observed using the VLT," says Schirmer.

"Ten minutes after the data were taken in Chile, I had them on my computer in Germany. I soon refocused my research activities entirely as it became apparent that I had come across something really new."

The new object, J2240, lies in the constellation of Aquarius (The Water Bearer) and its light has taken about 3.7 billion years to reach Earth.

After the discovery, Schirmer's team searched through a list of nearly a billion other galaxies and found 16 more with similar properties, which were confirmed by observations made at the Gemini South telescope.

General Background

In many galaxies the material around the supermassive black hole at the centre gives off intense radiation and ionises the surrounding gas so that it glows strongly.

These glowing regions in typical active galaxies are usually small, up to 10% of the diameter of the galaxy. However, the team's observations showed that in the case of J2240, and other green beans spotted since, it is truly huge, spanning the entire object.

J2240 displays one of the biggest and brightest such regions ever found. Ionised oxygen glows bright green, which explains the strange colour that originally caught Schirmer's attention.

"These glowing regions are fantastic probes to try to understand the physics of galaxies -- it's like sticking a medical thermometer into a galaxy far, far away," says Schirmer.

"Usually, these regions are neither very large nor very bright, and can only be seen well in nearby galaxies.

However, in these newly discovered galaxies they are so huge and bright that they can be observed in great detail, despite their large distances."

Giant black hole in tiny galaxy puzzles astronomers

Astronomers have spotted an enormous black hole - the second most massive ever - but it resides in a tiny galaxy.

The galaxy NGC 1277, just a quarter the size of our own Milky Way, hosts a black hole 4,000 times larger than the one at the Milky Way's centre.

A report in Nature shows it has a mass some 17 billion times that of our Sun.

The surprise finding is hard to reconcile with existing models of black hole growth, which hold that they evolve in tandem with host galaxies.

Getting to grips with just how large black holes are is a tricky business - after all, since they swallow light in their vicinities, they cannot be seen.

Instead, astronomers measure the black holes' "sphere of influence" - the gravitational effects they have on surrounding gas and stars.

In the Milky Way, it is possible to observe individual stars as they orbit Sagittarius A, our own local black hole, to guess its mass.

But for the 100 or so far more distant black holes whose masses have been estimated, astronomers have made average measurements of associated stars' speeds - their "velocity dispersion".

On a hunt for the Universe's largest black holes, astronomers using the Hobby-Eberly Telescope in the US state of Texas undertook a survey that brought in a haul of nearly 900 host galaxies.
 
'Big jigsaw'
But Remco van den Bosch, then at the University of Texas at Austin, and his colleagues were surprised to find that some of the largest black holes were to be found in small galaxies.

Among them was NGC 1277, 220 million light years away in the constellation Perseus, which happens to appear also in a high-resolution Hubble Space Telescope image, helping the researchers to refine their computer models.

"We make a model of the galaxy and compute all the possible stellar orbits," Dr Van den Bosch, who is now at the Max Planck Institute for Astronomy in Germany, explained.

Like a big jigsaw, we try to put those orbits together to reproduce that galaxy so it has the same stellar velocities we measure. "

What the team found was that the NGC 1277 black hole was enormous - as large as our Solar System, and comprising some 14% of the entire galaxy's mass.

"The only way to you can actually make those high dispersions in the centre is by having that really big black hole, there's really no other way around it," Dr Van den Bosch said.

What is more, the team have five other small-galaxy candidates that, with the help of more data, could disprove the rule that big black holes only happen in big galaxies.

But NGC 1277 is stranger still, and could help advance our theories of how black holes evolve in the first place.

"This galaxy seems to be very old," Dr Van den Bosch said. "So somehow this black hole grew very quickly a long time ago, but since then that galaxy has been sitting there not forming any new stars or anything else.

"We're trying to figure out how this happens, and we don't have an answer for that yet. But that's why it's cool."

M51: The Whirlpool Galaxy

Follow the handle of the Big Dipper away from the dipper's bowl until you get to the handle's last bright star.

Then, just slide your telescope a little south and west and you might find this stunning pair of interacting galaxies, the 51st entry in Charles Messier famous catalogue.

Perhaps the original spiral nebula, the large galaxy with well defined spiral structure is also catalogued as NGC 5194.

Its spiral arms and dust lanes clearly sweep in front of its companion galaxy (top), NGC 5195.

The pair are about 31 million light-years distant and officially lie within the angular boundaries of the small constellation Canes Venatici.

Though M51 looks faint and fuzzy to the human eye, deep images like this one can reveal the faint tidal debris around the smaller galaxy.

Nice but Dim: A bevy of stars found beyond our Milky Way

The Muñoz 1 globular cluster is seen to the right of the Ursa Minor dwarf galaxy in this image from the Canada-France-Hawaii Telescope MegaCam imager. Credit: Geha & Muñoz

A team of American, Canadian and Chilean astronomers have stumbled onto a remarkably faint cluster of stars orbiting the Milky Way that puts out as much light as only 120 modest Sun-like stars.

The tiny cluster, called Muñoz 1, was discovered near a dwarf galaxy in a survey of satellites around the Milky Way using the Canada-France-Hawaii Telescope (CFHT) and confirmed using the Keck II telescope, both of which are on Mauna Kea, Hawaii.

“What’s neat about this is it’s the dimmest globular cluster ever found,” said Ricardo Muñoz, an astronomer at the University of Chile and the discoverer of the cluster. A globular cluster is a spherical group of stars bound to each other by gravity so that they orbit around a galaxy as a unit.

“While I was working on the Ursa Minor dwarf galaxy I noticed there was this tiny little object close by,” Muñoz recalled. He made the discovery while he was a postdoctoral associate at Yale University.

Most globular clusters have in the range of 100,000 stars. Muñoz 1 has something like 500 stars. “This is very surprising,” he said.

“It’s ridiculously dim,” agreed Yale astronomer Marla Geha. “There are individual stars that would far outshine this entire globular cluster.” That puts Muñoz 1 head-to-head with the Segue 3 globular cluster (also orbiting the Milky Way) as the dimmest troupe of old stars ever found.

Muñoz 1’s discovery was the result of a survey done with the CFHT MegaCam imager in 2009 and 2010. It was then confirmed by spectroscopic study using the Deep Extragalactic Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II telescope. The researchers will be publishing their results soon in The Astrophysical Journal Letters.

SLAC’s New KIPAC Tool Gives Scientists a Closer Look at Merging Galaxies

Hubble Space Telescope image of two galaxies merging. This system is known as the “Antennae Galaxies.” (Image courtesy Hubble Space Telescope)

Scientists at SLAC’s Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) have created sophisticated computer simulations that show galaxy mergers in much more detail than ever before.

On large cosmic scales, galaxies are the fundamental “molecular” units that occupy much of space.

Understanding how they gravitationally interact is an important part of astrophysical research, since they can help explain star formation and other phenomena.

Central black holes in some galaxies, for example, create huge jets of energy, a mysterious activity that intrigues researchers.

Mergers between galaxies are rare. Based on its relatively undisturbed structure, we can estimate that our own Milky Way galaxy has not been part of any major mergers within the last 10 billion years.

When they do happen, they can produce some of the most awe-inspiring images from space. Such events may completely change the size and shape of galaxies, disrupting spiral arms and funneling stars into central bulges.

Individual stars are so far apart from each other, however, that an actual collision between two of them is extremely unlikely.

It is difficult to completely resolve the details of two interacting galaxies simply by observing them.

So scientists devise computer simulations of millions of galaxies evolving through the history of the universe, hoping to see mergers in process.

Impossible to manage by hand, the immense amount of detail involved in these simulations requires special tools for tracking clusters of galactic matter over time.

However, current analysis tools can’t differentiate the uniquely individual parts of galaxies during a merger, so the most interesting fine details are lost as the two galaxies become one.

To solve this problem, KIPAC graduate student Peter Behroozi, along with Professor Risa Wechsler and recent KIPAC alumna Heidi Wu, developed a new computational algorithm that uses both position and velocity information to distinguish galaxies in simulations.

The algorithm’s formal name is Robust Overdensity Calculation using K-Space Topologically Adaptive Refinement (ROCKSTAR - Pdf).

In essence, the program accounts for the speed, location and direction of the galactic elements. The result is a highly detailed picture of galaxy formation and disruption.

By extension, the algorithm’s measurement of galactic motions will also contribute to the larger study of the mass and energy content of the universe.

This work is based in part on a paper submitted to The Astrophysical Journal, online now on arXiv, and on an article by Peter Behroozi and Jack Singal for the KIPAC “Tidbits” newsletter.

Chandra and Hubble: Discovery of the Musket Ball Cluster

This composite image shows Chandra (red) and Hubble (yellow and white) data of the galaxy cluster system that has been nicknamed the "Musket Ball" cluster.

Astronomers call it this because the newly discovered cluster is older and slower than the Bullet Cluster, a famous system in which "normal" matter has been wrenched apart from dark matter.

Chandra detects the normal matter as hot gas, while optical emission reveals the presence of dark matter through the effect of gravitational lensing (blue).

The MusketBall Cluster or DLSCL J0916.2+2951, as it is officially known, is further along in its evolution than the Bullet Cluster, giving scientists valuable insight into a different phase of how galaxy clusters, the largest known objects held together by gravity, grow and change after major collisions.

Credit: X-ray: NASA/CXC/UCDavis/W.Dawson et al; Optical: NASA/STScI/UCDavis/W.Dawson et al.

Using a combination of powerful observatories in space and on the ground, astronomers have observed a violent collision between two galaxy clusters in which so-called normal matter has been wrenched apart from dark matter through a violent collision between two galaxy clusters.



The newly discovered galaxy cluster is called DLSCL J0916.2+2951. It is similar to the Bullet Cluster, the first system in which the separation of dark and normal matter was observed, but with some important differences.

The newly discovered system has been nicknamed the "Musket Ball Cluster" because the cluster collision is older and slower than the Bullet Cluster.

Finding another system that is further along in its evolution than the Bullet Cluster gives scientists valuable insight into a different phase of how galaxy clusters - the largest known objects held together by gravity - grow and change after major collisions.



Researchers used observations from NASA's Chandra X-ray Observatory and Hubble Space Telescope as well as the Keck, Subaru and Kitt Peak Mayall telescopes to show that hot, X-ray bright gas in the Musket Ball Cluster has been clearly separated from dark matter and galaxies.



In this composite image, the hot gas observed with Chandra is colored red, and the galaxies in the optical image from Hubble appear as mostly white and yellow.

The location of the majority of the matter in the cluster (dominated by dark matter) is colored blue. When the red and the blue regions overlap, the result is purple as seen in the image.

The matter distribution is determined by using data from Subaru, Hubble and the Mayall telescope that reveal the effects of gravitational lensing, an effect predicted by Einstein where large masses can distort the light from distant objects.

In addition to the Bullet Cluster, five other similar examples of merging clusters with separation between normal and dark matter and varying levels of complexity, have previously been found.

In these six systems, the collision is estimated to have occurred between 170 million and 250 million years earlier.

Read More here at Chandra X-Ray Centre 

NASA Hubble Space Telescope Image: The "UFO Galaxy."

Image Credit: ESA/Hubble & NASA

The NASA/ESA Hubble Space Telescope has spotted the "UFO Galaxy."

NGC 2683 is a spiral galaxy seen almost edge-on, giving it the shape of a classic science fiction spaceship.

This is why the astronomers at the Astronaut Memorial Planetarium and Observatory, Cocoa, Fla., gave it this attention-grabbing nickname.

While a bird's eye view lets us see the detailed structure of a galaxy (such as this Hubble image of a barred spiral), a side-on view has its own perks.

In particular, it gives astronomers a great opportunity to see the delicate dusty lanes of the spiral arms silhouetted against the golden haze of the galaxy’s core.

In addition, brilliant clusters of young blue stars shine scattered throughout the disc, mapping the galaxy’s star-forming regions.

Perhaps surprisingly, side-on views of galaxies like this one do not prevent astronomers from deducing their structures.

Studies of the properties of the light coming from NGC 2683 suggest that this is a barred spiral galaxy, even though the angle we see it at does not let us see this directly.

This image is produced from two adjacent fields observed in visible and infrared light by Hubble’s Advanced Camera for Surveys.

A narrow strip which appears slightly blurred and crosses most the image horizontally is a result of a gap between Hubble’s detectors.

This strip has been patched using images from observations of the galaxy made by ground-based telescopes, which show significantly less detail. The field of view is approximately 6.5 by 3.3 arcminutes.

Markarian Chain: A stretch of galaxies in the Virgo cluster

Credit: Larry Van VleetThis stunning image by skywatcher Larry Van Vleet is of Markarian's Chain, a stretch of galaxies in the Virgo cluster.

The galaxies are said to be in a smooth, curved line making them appear to be connected in a chain.

Located about 70 million light-years away, the Virgo cluster is a large collection of some 2,000 galaxies that dominate our part of the universe.

A light-year is the distance light travels in one year, or about 6 trillion miles (10 trillion kilometers).

Lynd's Dark Nebula: The Native American Woman Dancer

Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona

Resembling a dancer twirling her skirt in the wind, this image of the Lynd's Dark Nebula (LDN 1622) glows with deep blue and maroon colors.

The picture was taken by skywatcher and photographer Adam Block from the University of Arizona's Mt. Lemmon Sky Center.

LDN 1622 is called a dark nebula because interstellar dust is so thick it obscures light from nearby stars or other nebulas.

It is located near the plane of our Milky Way Galaxy close the Belt and Sword of Orion, an area that can be a favorite observing ground for avid skywatchers.

"My first impression of this nebula, especially looking at the raw grayscale images, was of a Native American woman dancer. She makes a cloud of dust as she twists in her movement. Perhaps I am influenced by where I reside, but the impressionistic form seems sinuous and kinetic," Block reported.

Canes Venatici: New Subaru Telescope images capture 'stealth merger' of dwarf galaxies

NGC 4449 is located 12.5 million light-years from Earth and is a member of a group of galaxies in the constellation Canes Venatici. In size and morphology, it is very similar to one of the Milky Way's satellite galaxies, the Large Magellanic Cloud.

New images of a nearby dwarf galaxy have revealed a dense stream of stars in its outer regions, the remains of an even smaller companion galaxy in the process of merging with its host.

The host galaxy, known as NGC 4449, is the smallest primary galaxy in which a stellar stream from an ongoing merger has been identified and studied in detail.

"This is how galaxies grow. You can see the smaller galaxy coming in and getting shredded, eventually leaving its stars scattered through the halo of the host galaxy," said Aaron Romanowsky, a research astronomer at the University of California, Santa Cruz, and coauthor of a paper on the discovery that has been accepted for publication in Astrophysical Journal Letters and is available online at arxiv.org.

The study was carried out by an international team of astronomers led by David Martinez-Delgado of the Max Planck Institute for Astronomy in Heidelberg.

Suprime-Cam captured this image of the nearby dwarf galaxy NGC 4449 (lower left) and its companion (upper right), a dwarf galaxy that has been gravitationally pulled apart into a stellar stream. It shows individual stars composing the galaxies. 

R. Jay GaBany (Blackbird Observatory) produced the composite: blue hues in the center of the larger galaxy are brought about by a burst of recent star formation, while the red in its periphery and in its satellite indicates the presence of older, red-giant stars.

 

According to modern cosmological theory, large galaxies were built up from smaller progenitors through a hierarchical process of mergers. Astronomers can see many examples of mergers involving massive galaxies, but mergers of two dwarf galaxies have been hard to find.

"We should see the same things at smaller scales, with small galaxies eating smaller ones and so on," Romanowsky said. "Now we have this beautiful image of a dwarf galaxy consuming a smaller dwarf."

NGC 4449 is located 12.5 million light-years from Earth and is a member of a group of galaxies in the constellation Canes Venatici. In size and morphology, it is very similar to one of the Milky Way's satellite galaxies, the Large Magellanic Cloud.

The stellar stream in NGC 4449 was first detected by another group of astronomers as a mysterious, faint smudge in digitized photographic plates from the Digitized Sky Survey project, and it is also visible in archival images from the Sloan Digital Sky Survey. But if it had been just a bit fainter, more diffuse, or farther from the host galaxy, it could easily have been missed.

The authors of the new study called it a "stealth merger," where an infalling satellite galaxy is nearly undetectable by conventional means, yet has a substantial influence on its host galaxy.

Read more of this article here

Hubble Zooms in on a Magnified Galaxy

Thanks to the presence of a natural "zoom lens" in space, this is a close-up look at brightest distant "magnified" galaxy in the universe known to date.

It is one of the most striking examples of gravitational lensing, where the gravitational field of a foreground galaxy bends and amplifies the light of a more distant background galaxy.

In this image the light from a distant galaxy, nearly 10 billion light-years away, has been warped into a nearly 90-degree arc of light in the galaxy cluster RCS2 032727-132623. 

The galaxy cluster lies 5 billion light-years away.

The background galaxy's image is 20 times larger and over three times brighter than typically lensed galaxies. 

The natural colour image was taken in March 2011 with the Hubble Space Telescope's Wide Field Camera 3. Credit: NASA; ESA; J. Rigby (NASA Goddard Space Flight Center); and K. Sharon (Kavli Institute for Cosmological Physics, University of Chicago).

NASA IBEX: Video - Glimpses of the Interstellar Material Beyond our Solar System

A great magnetic bubble surrounds the solar system as it cruises through the galaxy.

The sun pumps the inside of the bubble full of solar particles that stream out to the edge until they collide with the material that fills the rest of the galaxy, at a complex boundary called the heliosheath.

On the other side of the boundary, electrically charged particles from the galactic wind blow by, but rebound off the heliosheath, never to enter the solar system. Neutral particles, on the other hand, are a different story.

They saunter across the boundary as if it weren't there, continuing on another 7.5 billion miles for 30 years until they get caught by the sun's gravity, and sling shot around the star.

There, NASA's Interstellar Boundary Explorer lies in wait for them. Known as IBEX for short, this spacecraft methodically measures these samples of the mysterious neighbourhood beyond our home.

IBEX scans the entire sky once a year, and every February, its instruments point in the correct direction to intercept incoming neutral atoms.

IBEX counted those atoms in 2009 and 2010 and has now captured the best and most complete glimpse of the material that lies so far outside our own system.

The results? It's an alien environment out there: the material in that galactic wind doesn't look like the same stuff our solar system is made of.

ESO Mapping Dark Matter in Galaxies

A multitude of faint galaxies, small luminous dots scattered over the dark sky, was captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile.

Images such as this one are powerful tools to understand how dark matter is distributed in galaxies.

The picture is part of the COMBO-17 survey (Classifying Objects by Medium-Band Observations in 17 Filters), a project dedicated to recording detailed images of small patches of the sky through filters of 17 different colours.

The area covered in this image is only about the size of the full Moon, but thousands of galaxies can be identified just within this small region.

The image was taken with an exposure time of almost seven hours, which allowed the camera to capture the light from very faint and distant objects, as well as those that are closer to us.

Galaxies with clear and regular structures, such as the spiral specimen viewed edge-on near the upper left corner, are only up to a few billion light-years away. The fainter, fuzzier objects are so far away that it has taken nine or ten billion years for their light to reach us.

The COMBO-17 survey is a powerful tool for studying the distribution of dark matter in galaxies. Dark matter is a mysterious substance that does not emit or absorb light and can only be detected by its gravitational pull on other objects.

Some of the closer galaxies pictured act as lenses that distort the light coming from more distant galaxies placed along the same line of sight. By measuring this distortion, an effect known as gravitational lensing, astronomers are able to understand how dark matter is distributed in the objects that act as lenses.

The distortion is weak and, therefore, almost imperceptible to the human eye. However, because surveying the sky with 17 filters allows extremely precise distance measurements, it is possible to determine if two galaxies that appear to lie close to each other are actually at very different distances from the Earth.

After identifying the galactic lensing systems, the distortion can be measured by averaging over thousands of galaxies. With more than 4000 galactic lenses identified, this COMBO-17 survey is an ideal method to help astronomers to understand the dark matter better.

Links COMBO-17 at the Max Planck Institute for Astronomy
Credit: ESO

Astronomy Image: Sculptor Group of Galaxies

NGC 253 is not only one of the brightest spiral galaxies visible, it is also one of the dustiest.

Discovered in 1783 by Caroline Herschel in the constellation of Sculptor, NGC 253 lies only about ten million light-years distant. NGC 253 is the largest member of the Sculptor Group of Galaxies, the nearest group to our own Local Group of Galaxies.

The dense dark dust accompanies a high star formation rate, giving NGC 253 the designation of starburst galaxy. Visible in the above photograph is the active central nucleus, also known to be a bright source of X-rays and gamma rays.

Astrophotographer: Captures Colossal Pinwheel Galaxy

The Pinwheel Galaxy (also known as Messier 101 or NGC 5457) is estimated to contain at least one trillion stars, about 100 billion of them could be similar to our sun.

CREDIT: Thierry Legault

Equipped with an arsenal of telescopes and cameras, a French skywatching enthusiast had to venture beyond his suburban home in the so-called City of Lights to capture a brilliant deep-sky image of the Pinwheel Galaxy.

"I live in the suburbs of Paris, in a site that is very polluted by city lights," amateur astronomer Thierry Legault wrote on his website.

"From my backyard, I can take images of the sun, the moon, planets and nebulas with narrow band filters.

For deep sky imaging (galaxies, comets, nebulas...), I am obliged to go in the land, after loading my van."

The talented astrophotographer, who has become known for his eye-catching images, works as an engineer by day.

The Pinwheel Galaxy, which is also known as Messier 101 or NGC 5457, is a spiral galaxy 21 million light-years away in the constellation Ursa Major.

The galaxy was first discovered by Pierre Méchain on March 27, 1781. Charles Messier confirmed its position and it was included in the astronomer's famous Messier Catalogue as one of the final entries.

Double Comet Feature: Elenin & Garradd Now Showing in Night Sky

Skywatchers often ask "When's the next comet?" In fact, if you’re prepared to do a bit of searching, there are always several comets visible in the night sky, including two right now.

Some comets are like old friends, they keep coming back at regular intervals to visit.

These are called periodic comets; Comet Halley was the first such comet to be identified, by Edmond Halley back in 1705.

It returns to the inner solar system every 75 to 76 years; its last appearance was in 1986 and its next will be in 2061. At present Halley is out just beyond Neptune;s orbit.

NASA - Firestorm of Star Birth in the Active Galaxy Centaurus A

Resembling looming rain clouds on a stormy day, dark lanes of dust crisscross the giant elliptical galaxy Centaurus A.

Hubble's panchromatic vision, stretching from ultraviolet through near-infrared wavelengths, reveals the vibrant glow of young, blue star clusters and a glimpse into regions normally obscured by the dust.

The warped shape of Centaurus A's disk of gas and dust is evidence for a past collision and merger with another galaxy. The resulting shockwaves cause hydrogen gas clouds to compress, triggering a firestorm of new star formation. These are visible in the red patches in this Hubble close-up.

At a distance of just over 11 million light-years, Centaurus A contains the closest active galactic nucleus to Earth. The center is home for a supermassive black hole that ejects jets of high-speed gas into space, but neither the supermassive or the jets are visible in this image.

This image was taken in July 2010 with Hubble's Wide Field Camera 3.

The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA's Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI) conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

The Milky Way

The centre of our Galaxy is a busy place. In visible light, much of the Galactic Center is obscured by opaque dust.

In infrared light, however, dust glows more and obscures less, allowing nearly one million stars to be recorded in the above image.

The Galactic Centre itself appears glowing on the lower left and is located about 30,000 light years away towards the constellation of Sagittarius.

The Galactic Plane of our Milky Way Galaxy, the plane in which the Sun orbits, is identifiable by the dark diagonal dust lane.

The absorbing dust grains are created in the atmospheres of cool red-giant stars and grow in molecular clouds.

The region directly surrounding the Galactic Centre glows brightly in radio and high-energy radiation. The Galactic Centre is thought to house a large black hole.

NASA Hubble Space Telescope - The Universe's Most Ancient Object

The farthest and one of the very earliest galaxies ever seen in the universe appears as a faint red blob in this ultra-deep–field exposure taken with NASA's Hubble Space Telescope.

This is the deepest infrared image taken of the universe. Based on the object's color, astronomers believe it is 13.2 billion light-years away.

The most distant objects in the universe appear extremely red because their light is stretched to longer, redder wavelengths by the expansion of the universe.

This object is at an extremely faint magnitude of 29, which is 500 million times fainter that the faintest stars seen by the human eye.

The dim object is a compact galaxy of blue stars that existed 480 million years after the Big Bang, only four percent of the universe's current age. It is tiny and considered a building block of today's giant galaxies. Over one hundred such mini-galaxies would be needed to make up our Milky Way galaxy.

The Hubble Ultra Deep Field infrared exposures were taken in 2009 and 2010, and required a total of 111 orbits or 8 days of observing. The new Wide Field Camera 3 has the sharpness and near-infrared light sensitivity that matches the Advanced Camera for Surveys' optical images and allows for such a faint object to be selected from the thousands of other galaxies in the incredibly deep images of the Hubble Ultra Deep Field.

Credit: NASA, ESA, G. Illingworth (University of California, Santa Cruz), R. Bouwens (University of California, Santa Cruz and Leiden University), and the HUDF09 Team