*Description*: This loose collection of stars is actually a dwarf irregular galaxy, called Holmberg IX. It resides just off the outer edge of M81, a large spiral galaxy in Ursa Major. This image was taken with Hubble's Advanced Camera for Surveys in early 2006. Holmberg IX is of the so-called Magellanic type of galaxy, as its size and irregularity in structure are similar to the Small Magellanic Cloud, a neighbor to our own Milky Way. Holmberg IX was first discovered by astronomer Sidney van den Bergh in 1959, and cataloged as DDO 66. The galaxy received its "Holmberg IX" naming when it was discussed in Eric Holmberg's study of groups of galaxies ten years later. It is suspected that the dwarf galaxy was created as a result of a galactic interaction between M81 and neighboring galaxy M82. Of the more than 20,000 stars that can be resolved in this Hubble image, only about 10 percent are considered to be old stars with ages of billions of years. The rest are thought to be young stars with ages of only 10 to 200 million years. Due to the Advanced Camera for Surveys' resolution in this image, astronomers have noted that the old and the young stars have distinct spatial distributions which might be related to their origin. Simulations predict that the triplet M81, M82, and nearby NGC 3077 had a close passage 200 to 300 million years ago. This close encounter may have triggered the newer star formation that has occurred in Holmberg IX. The bluish-white fuzz in the space surrounding M81 and Holmberg IX is new star formation triggered by gravitational interactions between the two galaxies. There are many low mass galaxies that form stars in nearby space. While none of these are as dominated by recently produced stars as Holmberg IX, they might be related to the same family. By understanding how Holmberg IX was formed, scientists hope to understand their role as building blocks of large galaxies. Technical facts about this news release: About the Object Object Name: Arp's Loop, A0952+69 Holmberg IX, UGC 5336 Object Description: Collection of Blue Stars Dwarf Irregular Galaxy Position (J2000): R.A. 09h 57m 36.s08 Dec. 69° 16' 59."5 R.A. 09h 57m 40.s16 Dec. 69° 02' 55."4 Constellation: Ursa Major Ursa Major Distance: 12 million light-years (3.6 Megaparsecs) 12 million light-years (3.6 Megaparsecs) About the Data Science Team: The science team comprises D. de Mello (GSFC/Catholic University of America, Washington/JHU), L. Smith (STScI/ESA/University College London), E. Sabbi (STScI), J. Gallagher (University of Wisconsin, Madison), M. Mountain (STScI), and D. Harbeck (University of Wisconsin, Madison). Data Description: The Hubble image of Arp's Loop was created from HST data from proposal 10915: J. Dalcanton (University of Washington). The Hubble image of Holmberg IX was created from HST data from proposal 10605: E. Skillman (University of Minnesota, Twin Cities). Instrument: ACS/WFC ACS/WFC Exposure Date(s): September 22, 2006 March 23, 2006 Filters: F435W (B) and F814W (I) F555W (V) and F814W (I) About the Image Image Credit: NASA, ESA, and D. de Mello (Catholic University of America and GSFC) NASA, ESA, and the Hubble Heritage Team (STScI/AURA) Release Date: January 8, 2008 January 8, 2008 Color: These images are a composite of separate exposures made by the ACS instrument on the Hubble Space Telescope. Two filters were used to sample broad wavelength ranges. The color results from assigning different hues (colors) to each monochromatic image. In this case, the assigned colors are: F435W (B) blue F435W (B) + F814W (I) green F814W (I) red F555W (V) cyan F814W (I) orange Orientation: [ http://imgsrc.hubblesite.org/hu/db/2008/02/images/b/formats/compass_large_web.jpg ] [ http://imgsrc.hubblesite.org/hu/db/2008/02/images/d/formats/compass_large_web.jpg ] What is Hubble Heritage? A monthly showcase of new and archival Hubble images. Go to the Heritage site. What is an American Astronomical Society Meeting release? A major news announcement issued at an American Astronomical Society meeting, the premier astronomy conference. Hubble Space Telescope's powerful vision has resolved strange objects nicknamed "blue blobs" and found them to be brilliant blue clusters of stars born in the swirls and eddies of a galactic smashup 200 million years ago. Such "blue blobs" weighing tens of thousands of solar masses have never been seen in detail before in such sparse locations, say researchers. The "blue blobs" are found along a wispy bridge of gas strung among three colliding galaxies, M81, M82, and NGC 3077, residing about 12 million light-years away from Earth. This is not the place astronomers expect to find star clusters, because the gas filaments were considered too thin to accumulate enough material to actually build these many stars. The star clusters in this diffuse structure might have formed from gas collisions and subsequent turbulence, which enhanced locally the density of the gas streams. Galaxy collisions were much more frequent in the early universe, so "blue blobs" should have been common. After the stars burned out or exploded, the heavier elements forged in their nuclear furnaces would have been ejected to enrich intergalactic space. Read more: * The Full Story [ http://hubblesite.org/newscenter/archive/releases/2008/02/full/ ] *News Release Number:*: STScI-2008-02d
