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Surprise dew drops for Spiderweb Galaxy

Astronomers using the ALMA telescope to study the Spiderweb Galaxy unexpectedly found droplets of condensed water at the galaxy’s outskirts.

The Spiderweb Galaxy as seen by the Hubble Space Telescope (optical) in red, the Very Large Array (radio) in green and the Atacama Large Millimeter/submillimeter Array (submillimeter) in blue.  See annotated image below. Image via NASA, ESA-Hubble, STScI, NRAO, ESO.

The Spiderweb Galaxy as seen by the Hubble Space Telescope (optical) in red, the Very Large Array (radio) in green and the Atacama Large Millimeter/submillimeter Array (submillimeter) in blue. See annotated image below. Image via NASA, ESA-Hubble, STScI, NRAO, ESO.

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) to peer at the distant, very massive Spiderweb Galaxy expected to find droplets of condensed water in the galaxy’s central, dusty, star-forming regions. Instead, they found that the water is located in the galaxy’s outskirts. This result might provide clues to the processes that trigger star formation in some galaxies; in the case of the Spiderweb, known radio jets might play a role. Astronomer Bitten Gullberg presented these results yesterday (July 1, 2016) at the National Astronomy Meeting 2016 in Nottingham, England. She said:

The results are quite unexpected in that we’ve found that the water is located nowhere near the dusty stellar nurseries.

Observations of light emitted by water and by dust often go hand-in-hand. We usually interpret them as an insight into star-forming regions, with the illumination from young stars warming dust particles and water molecules until they start to glow.

Now … for the first time, we can separate out the emissions from the dust and water populations, and pinpoint their exact origins in the galaxy.

The new observations are made possible by the ALMA telescope in northern Chile, whose website describes it as “a single telescope of revolutionary design,” composed of 66 high-precision antennas. The telescope is located on the Chajnantor plateau, more than 16,000 feet (5,000 meters) above sea level.

This image is a composite of many separate exposures made by the ACS instrument on the Hubble Space Telescope. Image via ESA.

Hubble Space Telescope composite image of the Spiderweb Galaxy, aka MRC 1138-262. It sits at the center of an emergent galaxy cluster, surrounded by hundreds of other galaxies. Image via ESA.

The astronomers’ statement said:

The Spiderweb Galaxy is one of the most massive galaxies known. It lies 10 billion light-years away and is made up of dozens of star-forming galaxies in the process of merging together. The ALMA observations show that the light from the dust originates in the Spiderweb Galaxy itself. However, the light from the water is concentrated in two regions far to the east and west of the galaxy core.

Gullberg and her colleagues believe that the explanation lies with powerful jets of radio waves that are ejected from a supermassive black hole at the center of the Spiderweb Galaxy. The radio jets compress clouds of gas along their path and heat up water molecules contained within the clouds until they emit radiation.

Gullberg added:

Our results show how important it is to pinpoint the exact locations and origins for light in galaxies. We may also have new clues to the processes that trigger star formation in interstellar clouds.

Stars are born out of cold, dense molecular gas. The regions in the Spiderweb where we’ve detected water are currently too hot for stars to form. But the interaction with the radio jets changes the composition of the gas clouds. When the molecules have cooled down again, it will be possible for the seeds of new stars to form.

These ‘dew drop’ regions could become the next stellar nurseries in this massive, complex galaxy.

The red color shows where the stars are located within this system of galaxies. The radio jet is shown in green, and the position of the dust and water are seen in blue. The water is located to the left and right of the central galaxy. The water to the right is at the position where the radio jet bends down wards. The dust is also seen in blue. The dust is located at the central galaxy and in smaller companion galaxies in its surroundings. Image via NASA, ESA-Hubble, STScI, NRAO, ESO.

The red color shows where the stars are located within this system of galaxies. The radio jet is shown in green, and the position of the dust and water are seen in blue. The water is located to the left and right of the central galaxy. The water to the right is at the position where the radio jet bends down wards. The dust is also seen in blue. The dust is located at the central galaxy and in smaller companion galaxies in its surroundings. Image via NASA, ESA-Hubble, STScI, NRAO, ESO.

Bottom line: Astronomers using ALMA to study the Spiderweb Galaxy, aka MRC 1138-262, unexpectedly found water droplets at the galaxy’s outskirts.

Deborah Byrd

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