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A "Rose" Made of Galaxies Highlights Hubble's 21st Anniversary.
In celebration of the 21st anniversary of the Hubble Space Telescope's deployment into space, astronomers at the
Space Telescope Science Institute in Baltimore, Md., pointed Hubble's eye to an especially photogenic group of
interacting galaxies called Arp 273.
The larger of the spiral galaxies, known as UGC 1810, has a disk that is tidally distorted into a rose-like shape by the
gravitational tidal pull of the companion galaxy below it, known as UGC 1813. A swath of blue jewels across the top is
the combined light from clusters of intensely bright and hot young blue stars. These massive stars glow fiercely in
The smaller, nearly edge-on companion shows distinct signs of intense star formation at its nucleus, perhaps triggered
by the encounter with the companion galaxy.
A series of uncommon spiral patterns in the large galaxy is a tell-tale sign of interaction. The large, outer arm appears
partially as a ring, a feature seen when interacting galaxies actually pass through one another. This suggests that the
smaller companion actually dived deep, but off-center, through UGC 1810. The inner set of spiral arms is highly warped
out of the plane with one of the arms going behind the bulge and coming back out the other side. How these two spiral
patterns connect is still not precisely known.
A possible mini-spiral may be visible in the spiral arms of UGC 1810 to the upper right. It is noticeable how the outermost
spiral arm changes character as it passes this third galaxy, from smooth with lots of old stars (reddish in color) on one
side to clumpy and extremely blue on the other. The fairly regular spacing of the blue star-forming knots fits with what is
seen in the spiral arms of other galaxies and is predictable based on instabilities in the gas contained within the arm.
The larger galaxy in the UGC 1810 - UGC 1813 pair has a mass that is about five times that of the smaller galaxy. In
unequal pairs such as this, the relatively rapid passage of a companion galaxy produces the lopsided or asymmetric
structure in the main spiral. Also in such encounters, the starburst activity typically begins in the minor galaxies earlier
than in the major galaxies. These effects could be due to the fact that the smaller galaxies have consumed less of the
gas present in their nucleus, from which new stars are born.
Arp 273 lies in the constellation Andromeda and is roughly 300 million light-years away from Earth. The image shows a
tenuous tidal bridge of material between the two galaxies that are separated by tens of thousands of light-years from
The interaction was imaged on December 17, 2010, with Hubble's Wide Field Camera 3 (WFC3).
This Hubble image is a composite of data taken with three separate filters on WFC3 that allow a broad range of
wavelengths covering the ultraviolet, blue, and red portions of the spectrum.
Release date: April 20, 2011
Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)