Study of galaxy reveals ‘football-shaped’ bulge

Friday 12 January 2007

Scientists at the University of St Andrews have carried out a new study of one of the oldest parts of the Galaxy. The collaboration between astronomers at St Andrews and UCLA (University of California Los Angeles) is the largest survey to date of the speed of stars within the ‘Galactic bulge’.

The researchers measured the speeds of nearly 3,000 stars found 1,500 light years away from the Galactic Centre. The Galactic bulge, some 25,000 light years from the sun, is one of the oldest parts of the Galaxy and contains roughly 20 billion suns. Recent studies suggest that the bulge formed relatively quickly and was one of the first parts of the Galaxy to form.

Using a combination of computer modeling developed by Dr HongSheng Zhao at St Andrews and telescopic observations from Chile, researchers were surprised to find a spinning, American football- shaped bulge (also known as the Galactic bar).

Dr Zhao, a reader at the School of Physics and Astronomy at St Andrews and member of the Scottish Universities Physics Alliance (SUPA), said, “The bulge has the shape it does because its stars follow orbits around the center of the Milky Way. Some of these orbits are familiar circles, like the planets of our solar systems, but others follow strange loops or long ellipses.”

Their survey also reveals many groups of stars moving at around the same speed. The researchers believe that these ‘clumps’ of stars may be the fossil remnants of star clusters or dwarf galaxies that fell into the bulge and are in the process of dissolving.

Further work may enable the team gain further understanding into how the football-shaped bulge was assembled in the first place.

“A better knowledge of the orbits of bulge stars may help to predict how many stars might interact or fall into the central black hole of the Milky Way; the spectacular explosion associated with that event, a capture flare, has been observed to occur in other galaxies,” Dr. Rich explained.

Supported by NASA and the National Science Foundation, the survey was conducted rapidly, in only eight nights of observing time over the last two years. Using the Hydra spectrograph and new techniques developed by UCLA, researchers could observe speeds of 100 stars simultaneously using optical fibres.

The study, carried out by Dr Zhao and UCLA’s Drs. R. Michael Rich and David Reitzel, will be presented at the American Astronomical Society meeting in Seattle, Washington this week.




ST ANDREWS Dr. HongSheng Zhao hz4@st-, mobile: 00 86 1352 2871424 (currently in Bejing), thereafter on 07786 968505.

UCLA Dr. R. Michael Rich, Tel: (310) 794-5337 Mobile: (310) 775-5138 [email protected] Dr. David B. Reitzel, Tel: (310) 825-3845 Mobile: (310) 666-5372 [email protected] Christian Howard, Tel: (310) 825- 3172 [email protected]

Images and more information at: el/BRAVA.html



Issued by the Press Office of the University of St Andrews

Contact Gayle Cook, Press Officer on 01334 467227 / 462529, mobile 07900 050 103, or email gec3@st-

Ref: Galaxy Bulge 120107.doc

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