Anne’s Picture of the Day: LH 72

read more at Anne’s Astronomy News http://annesastronomynews.com/

October 25, 2012

LH 72, a small group of stars embedded in a nebula in the LMC

Image Credit: ESA/Hubble, NASA and D. A. Gouliermis

LH 72 is a young and bright OB association embedded in a dense nebula of hydrogen gas, located about 160,000 light-years away in one of the largest known star-forming regions in the Large Magellanic Cloud (a small irregular satellite galaxy of our Milky Way galaxy) in the constellation Dorado.

An OB association is a loosely organized stellar grouping that usually contains 10–100 stars of type O and B — these are high-mass stars that have short but brilliant lives. There are several such groupings of stars in the Large Magellanic Cloud. Just like the others, LH 72 consists of several high-mass young stars with ages ranging from 5 to 30 million years. Their ages are increasing from the south to the north end of LH 72. The OB association lies in a supergiant shell of gas called LMC-4.

Much of the star formation in the Large Magellanic Cloud occurs in such supergiant shells. These regions of interstellar gas are thought to have formed due to strong stellar winds and supernova explosions that blew away dust and gas around the stars creating wind-blown shells. The swept-up gas eventually cools down and fragments into smaller clouds that dot the edges of these regions and eventually collapse to form new stars. Over a period of several million years, thousands of stars may form in these supergiant shells, which are the largest interstellar structures in galaxies.

LMC-4 is, with a diameter of about 6000 light-years, the biggest of these shells, and it is also the largest in the Local Group of galaxies that is home to both the Milky Way and the Large Magellanic Cloud.

LH 72 is the only OB association embedded in significant amounts of ionized neutral gas that lies within LMC-4. Thus, LH 72 may hold a special clue to LMC-4’s formation. Studying gas-embedded young associations of stars like LH 72 is a way of probing the supergiant shells to understand how they formed and evolved.

This image was taken with Hubble’s Wide Field Planetary Camera 2 using five different filters in ultraviolet, visible and infrared light.

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