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ESO�s Very Large Telescope (VLT) has captured a magnificent face-on view of the barred spiral galaxy Messier 77. The image does justice to the galaxy�s beauty, showcasing its glittering arms criss-crossed with dust lanes � but it fails to betray Messier 77�s turbulent nature.

This picturesque spiral galaxy appears to be tranquil, but there is more to it than meets the eye. Messier 77 (also known as NGC 1068) is one of the closest active galaxies, which are some of the most energetic and spectacular objects in the Universe. Their nuclei are often bright enough to outshine the whole of the rest of the galaxy. Active galaxies are among the brightest objects in the Universe and emit light at most, if not all, wavelengths, from gamma rays and X-rays all the way to microwaves and radiowaves. Messier 77 is further classified as a Type II Seyfert galaxy, characterised by being particularly bright at infrared wavelengths.

This impressive luminosity is caused by intense radiation blasting out from a central engine � the accretion disc surrounding a supermassive black hole. Material that falls towards the black hole is compressed and heated up to incredible temperatures, causing it to radiate a tremendous amount of energy. This accretion disc is thought to be enshrouded by thick doughnut-shaped structure of gas and dust, called a �torus�. Observations of Messier 77 back in 2003 were the first to resolve such a structure using the powerful VLT Interferometer.

This image of Messier 77 was taken in four different wavelength bands represented by blue, red, violet and pink (hydrogen-alpha) colours. Each wavelength brings out a different quality: for example, the pinkish hydrogen-alpha highlights the hotter and younger stars forming in the spiral arms, while in red are the fine, thread-like filamentary structures in the gas surrounding Messier 77. A foreground Milky Way star is also seen beside the galaxy centre, displaying tell-tale diffraction spikes. Additionally, many more distant galaxies are visible; sitting at the outskirts of the spiral arms, they appear tiny and delicate compared to the colossal active galaxy .

Located 47 million light-years away in the constellation of Cetus (The Sea Monster), Messier 77 is one of the most remote galaxies of the Messier catalogue. Initially, Messier believed that the highly luminous object he saw through his telescope was a cluster of stars, but as technology progressed its true status as a galaxy was realised. At approximately 100 000 light-years across, Messier 77 is also one of largest galaxies in the Messier catalogue � so massive that its gravity causes other nearby galaxies to twist and become warped.

This image was obtained using the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument mounted on Unit Telescope 1 (Antu) of the VLT, located at ESO�s Paranal Observatory in Chile. It hails from ESO�s Cosmic Gems programme, an outreach initiative that produces images of interesting, intriguing or visually attractive objects using ESO telescopes for the purposes of education and outreach.

This beautiful galaxy is tilted at an oblique angle on to our line of sight, giving a "birds-eye view" of the spiral structure. The galaxy is similar to our Milky Way, but our favorable view provides a better picture of the typical architecture of spiral galaxies.

M81 may be undergoing a surge of star formation along the spiral arms due to a close encounter it may have had with its nearby spiral galaxy NGC 3077 and a nearby starburst galaxy (M82) about 300 million years ago.

M81 is one of the brightest galaxies that can be seen from the Earth. It is high in the northern sky in the circumpolar constellation Ursa Major, the Great Bear. At an apparent magnitude of 6.8 it is just at the limit of naked-eye visibility. The galaxys angular size is about the same as that of the Full Moon.

This image combines data from the Hubble Space Telescope, the Spitzer Space Telescope, and the Galaxy Evolution Explorer (GALEX) missions. The GALEX ultraviolet data were from the far-UV portion of the spectrum (135 to 175 nanometers). The Spitzer infrared data were taken with the IRAC channel 4 detector (8 microns). The Hubble data were taken at the blue portion of the spectrum.

Using a quartet of space observatories, University of Maryland astronomers may have cracked a 45-year mystery surrounding two ghostly spiral arms in the galaxy M106.

The Maryland team, led by Yuxuan Yang, took advantage of the unique capabilities of NASAs Chandra X-ray Observatory, NASAs Spitzer Space Telescope, the European Space Agencys XMM-Newton X-ray observatory, and data obtained almost a decade ago with NASAs Hubble Space Telescope.

M106 (also known as NGC 4258) is a stately spiral galaxy 23.5 million light-years away in the constellation Canes Venatici. In visible-light images, two prominent arms emanate from the bright nucleus and spiral outward. These arms are dominated by young, bright stars, which light up the gas within the arms. "But in radio and X-ray images, two additional spiral arms dominate the picture, appearing as ghostly apparitions between the main arms," says team member Andrew Wilson of the University of Maryland. These so-called "anomalous arms" consist mostly of gas.

"The nature of these anomalous arms is a long-standing puzzle in astronomy," says Yang. "They have been a mystery since they were first discovered in the early 1960s."

By analyzing data from XMM-Newton, Spitzer, and Chandra, Yang, Bo Li, Wilson, and Christopher Reynolds, all at the University of Maryland at College Park, have confirmed earlier suspicions that the ghostly arms represent regions of gas that are being violently heated by shock waves.

Previously, some astronomers had suggested that the anomalous arms are jets of particles being ejected by a supermassive black hole in M106s nucleus. But radio observations by the National Radio Astronomy Observatorys Very Long Baseline Array, and the Very Large Array in New Mexico, later identified another pair of jets originating in the core. "It is highly unlikely that an active galactic nucleus could have more than one pair of jets," says Yang.

In 2001, Wilson, Yang, and Gerald Cecil, of the University of North Carolina, Chapel Hill, noted that the two jets are tipped 30 degrees with respect to the galaxy disk. But if one could vertically project the jets onto the disk, they would line up almost perfectly with the anomalous arms. Figuring that this alignment was not strictly a matter of chance, Wilson, Yang, and Cecil proposed that the jets heat the gas in their line of travel, forming an expanding cocoon. Because the jets lie close to M106s disk, the cocoon heats gas in the disk and generates shock waves, heating the gas to millions of degrees and causing it to radiate brightly in X-rays and other wavelengths.

To test this idea, Yang and his colleagues looked at archival spectral observations from XMM-Newton. With XMM-Newtons superb sensitivity, the team could measure the gas temperature in the anomalous arms and also see how strongly X-rays from the gas are absorbed en route by intervening material.

"One of the predictions of this scenario is that the anomalous arms will gradually be pushed out of the galactic disk plane by jet-heated gas," says Yang. The XMM-Newton spectra show that X-rays are more strongly absorbed in the direction of the northwest arm than in the southeast arm. The results strongly suggest that the southeast arm is partly on the near side of M106s disk, and the northwest arm is partly on the far side.

The scientists noted that these observations show clear consistency with their scenario. Confirmation of this interpretation has recently come from archival observations from NASAs Spitzer Space Telescope, whose infrared view shows clear signs that X-ray emission from the northwest arm is being absorbed by warm gas and dust in the galaxys disk. Moreover, Chandras superior imaging resolution gives clear indications of gas shocked by interactions with the two jets.

Besides addressing the mystery of the anomalous arms, these observations allowed the team to estimate the energy in the jets and gauge their relationship to M106s central black hole.