A stunning new image captured by the NASA/ESA Hubble Space Telescope shows the lopsided intermediate spiral galaxy NGC 4654, whose unusual shape was sculpted by both a close encounter with another galaxy and a headlong plunge through the hot gas of the Virgo Cluster.
This Hubble image shows NGC 4654, an intermediate spiral galaxy some 55 million light-years away in the constellation of Virgo. Image credit: NASA / ESA / Hubble / D. Thilker / J. Lee / PHANGS-HST Team.
NGC 4654 is located approximately 55 million light-years away in the constellation of Virgo.
Also known IC 3708 or LEDA 42857, this galaxy has a diameter of about 70,000 light-years.
It was first discovered by the German-British astronomer William Herschel on April 12, 1784.
NGC 4654 is a member of the Virgo Cluster, a group of up to 2,000 galaxies.
“NGC 4654 is classified as an intermediate because its overall shape lies between spiral galaxies that have a bar across their centers and those that don’t,” the Hubble astronomers said in a statement.
“The galaxy is particularly asymmetric, with a rounded and clearly-defined edge on one side and a long tail of gas stretching out from the opposite side — outside the field of view captured in this image.”
“This gaseous tail is the result of ram-pressure stripping, a force that galaxies can experience as they plow through space.”
“NGC 4654 moves with such high velocity that it sweeps up and rams through the hot, rarefied gas filling the space between the Virgo Cluster’s galaxies,” they said.
“This intracluster medium in turn exerts a ram pressure on the galaxy, compressing the galaxy’s leading edge and dragging its gas behind the galaxy, creating the elongated tail.”
“It’s not just the galaxy’s gas that is unevenly distributed: its stars are too, and this is more unusual for a spiral galaxy.”
“While the spiral arm on its leading edge is rich with stars and gas, the opposite arm noticeably lacks stars, influencing the galaxy’s lopsided spiral shape.”
The astronomers think that ram pressure alone is unlikely to cause this effect.
“Rather, NGC 4654 was also subjected to the gravitational force of the fellow Virgo Cluster galaxy NGC 4639,” they said.
“While the two galaxies are far apart now, it’s thought that a fly-by interaction between them around 500 million years ago ripped away NGC 4654’s gas along one side, limiting star formation there and creating the asymmetry in its shape.”
“Many galaxies that undergo ram-pressure stripping suffer reduced star formation rates as the cold gas that collapses to form their stars is pulled away and lost,” the researchers explained.
“NGC 4654, however, is still forming nearly two Suns’ worth of stars every year, a rate comparable to other galaxies of similar size.”
“The active star formation is visible in the latest Hubble data included in this image.”
“The data pick up on a wavelength of red light emitted by the clouds of energized gas where newborn stars lurk.”
“The bright pink bubbles that appear across NGC 4654 — from its forward spiral arm, to around its weak bar, and out to the edge of its disk — are areas where these newborn stars shine.”
