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Monday, September 17, 2018

Globular Cluster NGC 2108

Globular Cluster NGC 2108
Click on the image for full resolution (5.5 MB)

This Picture of the Week shows the colourful globular cluster NGC 2108. The cluster is nestled within the Large Magellanic Cloud, in the constellation of the Swordfish (Dorado). It was discovered in 1835 by the astronomer, mathematician, chemist and inventor John Herschel, son of the famous William Herschel. The most striking feature of this globular cluster is the gleaming ruby-red spot at the center left of the cluster. What looks like the cluster's watchful eye is actually a carbon star. Carbon stars are almost always cool red giants, with atmospheres containing more carbon than oxygen – the opposite to our Sun. Carbon monoxide forms in the outer layer of the star through a combination of these elements, until there is no more oxygen available. Carbon atoms are then free to form a variety of other carbon compounds, such as C2, CH, CN, C3 and SiC2, which scatter blue light within the star, allowing red light to pass through undisturbed. This image was captured by the NASA/ESA Hubble Space Telescope's Advanced Camera for Surveys (ACS), using three different filters.
Image Credit: ESA/Hubble and NASA
Image enhancement: Jean-Baptiste Faure

Barred Spiral Galaxy NGC 1015

Barred Spiral Galaxy NGC 1015
Click on the image for full resolution (5.1 MB)

This stunning image from Hubble shows the majestic galaxy NGC 1015, found nestled within the constellation of Cetus (The Whale) 118 million light-years from Earth. In this image, we see NGC 1015 face-on, with its beautifully symmetrical swirling arms and bright central bulge creating a scene akin to a sparkling Catherine wheel firework. NGC 1015 has a bright, fairly large centre and smooth, tightly wound spiral arms and a central "bar" of gas and stars. This shape leads NGC 1015 to be classified as a barred spiral galaxy – just like our home, the Milky Way. Bars are found in around two-thirds of all spiral galaxies, and the arms of this galaxy swirl outwards from a pale yellow ring encircling the bar itself. Scientists believe that any hungry black holes lurking at the center of barred spirals funnel gas and energy from the outer arms into the core via these glowing bars, feeding the black hole, fueling star birth at the center and building up the galaxy's central bulge. In 2009, a Type Ia supernova named SN 2009ig was spotted in NGC 1015 – one of the bright dots to the upper right of the galaxy's center. These types of supernovae are extremely important: they are all caused by exploding white dwarfs which have companion stars, and always peak at the same brightness – 5 billion times brighter than the Sun. Knowing the true brightness of these events, and comparing this with their apparent brightness, gives astronomers a unique chance to measure distances in the Universe.
Image Credit: ESA/Hubble and NASA, A. Riess (STScl/JHU)
Image enhancement: Jean-Baptiste Faure

Sunday, September 16, 2018

Star-Forming Region Sharpless 29

Star-Forming Region Sharpless 29
Click on the image for full resolution (7.4 MB)

This image from the OmegaCAM imager on ESO's VLT Survey Telescope captures a glittering view of the stellar nursery called Sharpless 29. The region of sky pictured is listed in the Sharpless catalogue of H II regions: interstellar clouds of ionised gas, rife with star formation. Also known as Sh 2-29, Sharpless 29 is located about 5500 light-years away in the constellation of Sagittarius (The Archer), next door to the larger Lagoon Nebula. It contains many astronomical wonders, including the highly active star formation site of NGC 6559, the nebula at the center of the image. Many astronomical phenomena can be seen in this image, including cosmic dust and gas clouds that reflect, absorb, and re-emit the light of hot young stars within the nebula.
Image Credit: ESO
Image enhancement: Jean-Baptiste Faure

Protostar IRAS 20324+4057

Protostar IRAS 20324+4057
Click on the image for full resolution (1.0 MB)

This light-year-long knot of interstellar gas and dust resembles a caterpillar on its way to a feast. But the meat of the story is not only what this cosmic caterpillar eats for lunch, but also what's eating it. Harsh winds from extremely bright stars are blasting ultraviolet radiation at this "wanna-be" star and sculpting the gas and dust into its long shape. The culprits are 65 of the hottest, brightest known stars, classified as O-type stars, located 15 light-years away from the knot, towards the right edge of the image. These stars, along with 500 less bright, but still highly luminous, B-type stars make up what is called the Cygnus OB2 association. Collectively, the association is thought to have a mass more than 30 000 times that of our Sun.
The caterpillar-shaped knot, called IRAS 20324+4057, is a protostar in a very early evolutionary stage. It is still in the process of collecting material from an envelope of gas surrounding it. However, that envelope is being eroded by the radiation from Cygnus OB2. Protostars in this region should eventually become young stars with final masses about one to ten times that of our Sun, but if the eroding radiation from the nearby bright stars destroys the gas envelope before the protostars finish collecting mass, their final masses may be reduced. Spectroscopic observations of the central star within IRAS 20324+4057 show that it is still collecting material quite heavily from its outer envelope, hoping to bulk up. Only time will tell if the formed star will be a "heavy-weight" or a "light-weight" with respect to its mass.
This image of IRAS 20324+4057 is a composite of Hubble Advanced Camera for Surveys (ACS) data taken in green and infrared light in 2006, and ground-based hydrogen data from the Isaac Newton Telescope in 2003, as part of the IPHAS H-alpha survey. The object lies 4500 light-years away in the constellation of Cygnus (The Swan).
Image Credit: NASA, ESA, the Hubble Heritage Team (STScI/AURA), and IPHAS
Image enhancement: Jean-Baptiste Faure

Wednesday, February 7, 2018

Barred Spiral Galaxy UGC 6093

Barred Spiral Galaxy UGC 6093
Click on the image for full resolution (2.8 MB)

This image, captured by the Hubble Space Telescope's Wide Field Camera 3 (WFC3), shows a galaxy named UGC 6093. As can be easily seen, UGC 6093 is something known as a barred spiral galaxy – it has beautiful arms that swirl outwards from a bar slicing through the galaxy's center. It is classified as an active galaxy, which means that it hosts an active galactic nucleus, or AGN: a compact region at a galaxy's center within which material is dragged towards a supermassive black hole. As this black hole devours the surrounding matter it emits intense radiation, causing it to shine brightly.
But UGC 6093 is more exotic still. The galaxy essentially acts as a giant astronomical laser that spews out light at microwave, not visible, wavelengths – this type of object is dubbed a megamaser (maser being the term for a microwave laser). Megamasers such as UGC 6093 can be some 100 million times brighter than masers found in galaxies like the Milky Way.
Hubble's WFC3 observes light spanning a range wavelengths – from the near-infrared, through the visible range, to the near-ultraviolet. It has two channels that detect and process different light, allowing astronomers to study a remarkable range of astrophysical phenomena; for example, the UV-visible channel can study galaxies undergoing massive star formation, while the near-infrared channel can study redshifted light from galaxies in the distant Universe. Such multi-band imaging makes Hubble invaluable in studying megamaser galaxies, as it is able to untangle their intriguing complexity.
Image Credit: ESA/Hubble and NASA
Image enhancement: Jean-Baptiste Faure

Sunday, October 22, 2017

Spiral Galaxy NGC 4424

Spiral Galaxy NGC 4424
Click on the image for full resolution (4.1 MB)

Two galaxies are clearly visible in this Hubble image, the larger of which is NGC 4424. This galaxy is catalogued in the New General Catalogue of Nebulae and Clusters of Stars (NGC), which was compiled in 1888. The NGC is one of the largest astronomical catalogues, which is why so many Hubble Pictures of the Week feature NGC objects. In total there are 7840 entries in the catalogue and they are also generally the larger, brighter, and more eye-catching objects in the night sky, and hence the ones more easily spotted by early stargazers. The smaller, flatter, bright galaxy sitting just below NGC 4424 is named LEDA 213994. The Lyon-Meudon Extragalactic Database (LEDA) is far more modern than the NGC. Created in 1983 at the Lyon Observatory it contains millions of objects. However, many NGC objects still go by their initial names simply because they were christened within the NGC first. No astronomer can resist a good acronym, and "LEDA" is more appealing than "the LMED", perhaps thanks to the old astronomical affinity with mythology when it comes to naming things: Leda was a princess in Ancient Greek mythology.
Image Credit: ESA/Hubble and NASA
Image enhancement: Jean-Baptiste Faure

Saturday, May 20, 2017

Interacting Galaxies NGC 3447

Interacting Galaxies NGC 3447
Click on the image for full resolution (5.9 MB)

Some galaxies are harder to classify than others. Here, Hubble's trusty Wide Field Camera 3 (WFC3) has captured a striking view of two interacting galaxies located some 60 million light-years away in the constellation of Leo (The Lion). The more diffuse and patchy blue glow covering the right side of the frame is known as NGC 3447 – sometimes NGC 3447B for clarity, as the name NGC 3447 can apply to the overall duo. The smaller clump to the upper left is known as NGC 3447A. The trouble with space is that it is, to state the obvious, really, really big. Astronomers have for hundreds of years been discovering and naming galaxies, stars, cosmic clouds and more. Unifying and regulating the conventions and classifications for everything ever observed is very difficult, especially when you get an ambiguous object like NGC 3447, which stubbornly defies easy categorisation. Overall, we know NGC 3447 comprises a couple of interacting galaxies, but we're unsure what each looked like before they began to tear one another apart. The two sit so close that they are strongly influenced and distorted by the gravitational forces between them, causing the galaxies to twist themselves into the unusual and unique shapes seen here. NGC 3447A appears to display the remnants of a central bar structure and some disrupted spiral arms, both properties characteristic of certain spiral galaxies. Some identify NGC 3447B as a former spiral galaxy, while others categorise it as being an irregular galaxy.
Image Credit: ESA/Hubble and NASA
Image enhancement: Jean-Baptiste Faure