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Hot hydrogen reveals stellar birth, death and some interesting bits in between

posted Jul 15, 2014, 7:29 AM by Jeremy Drake   [ updated Jul 16, 2014, 12:41 AM ]
University of Hertfordshire professor Janet Drew is leading a large international project to survey the plane of our Galaxy in "H-alpha" light.  "H-alpha" is shorthand for a specific red light emitted by hydrogen atoms (in technical terms, when the bound electron transitions from n=3 to n=2 quantum levels).  H-alpha is emitted by hot nebulae, very young stars still accreting from their natal envelopes and disks, gas falling onto compact stars such as white dwarfs and neutron stars, and generally any object in which cosmic gas is illuminated by strong UV light, such as originates from massive, bright stars. Such objects are difficult to find in broad-band visible light, either because they are by nature rare, or because they represent a fleeting evolutionary phase and are quickly gone. A survey in H-alpha is a powerful way to find them and to assess our Galaxy's inventory of stellar birth, death, compact objects and ionized gas.

The northern hemisphere survey, "IPHAS", is essentially complete.  Efforts at present concentrate on the southern Galactic plane, including the Galactic Centre and "bulge" using the European Southern Observatory's rather confusingly named "Very Large Telescope Survey Telescope", or VST. Begun on 2011 December 28, the VST survey, "VPHAS+", observes the Galaxy in near-ultraviolet, green, red, near-infrared and H-alpha light.  It reaches down to approximately 20th magnitude and will provide multi-colour brightness measurements for about 300 million stars.  The initial survey data validation has just been completed, and a description of the project and its future promise was published in the 2014 April 2 edition of the Monthly Notices of the Royal Astronomical Society.