We Just Discovered a New Type of Colossal Galaxy

This new image of the spiral galaxy NGC 3521 from the NASA/ESA Hubble Space Telescope is not out of focus. Instead, the galaxy itself has a soft, woolly appearance as it a member of a class of galaxies known as flocculent spirals. Like other flocculent galaxies, NGC 3521 lacks the clearly defined, arcing structure to its spiral arms that shows up in galaxies such as Messier 101, which are called grand design spirals. In flocculent spirals, fluffy patches of stars and dust show up here and there throughout their discs. Sometimes the tufts of stars are arranged in a generally spiralling form, as with NGC 3521, but illuminated star-filled regions can also appear as short or discontinuous spiral arms. About 30 percent of galaxies share NGC 3521's patchiness, while approximately 10 percent have their star-forming regions wound into grand design spirals. NGC 3521 is located almost 40 million light-years away in the constellation of Leo (The Lion). The British astronomer William Herschel discovered the object in 1784. Through backyard telescopes, NGC 3521 can have a glowing, rounded appearance, giving rise to its nickname, the Bubble Galaxy. *Image: NASA*

Super Spirals

Astronomers from the California Institute of Technology have discovered a massive new kind of galaxy, which they now call a “super spiral.” These galaxies give off bright light that can shine up to 14 times that of the Milky Way Galaxy.

Simply put, super spirals are enormous.

They have diameters that can measure up to 437,000 light-years. For comparison, the Milky Way is just a little over 100,000 light-years across. And they can weigh up to 340 billion solar masses. The massive size also means that super spirals can give off an incredible amount of ultraviolet and mid-infrared light. To that end, the galaxy has a very high rate of star formation, generating new stars 30 times faster than our galaxy.

The discovery was made by a team of astronomers led by Dr. Patrick Ogle, who write that they had chanced upon the galaxies in the NASA/IPAC Extragalactic Database (NED) while in search of other extremely luminous and massive galaxies.

Co-author Dr. George Helou said: “Remarkably, the finding of super spiral galaxies came out of purely analyzing the contents of the NED database, thus reaping the benefits of the careful, systematic merging of data from many sources on the same galaxies.”

Data and Discovery

mages of super spiral galaxies. Examples with peculiar morphology: (1) multi-arm spiral, (8) asymmetric two-arm spiral, (21) ring galaxy, (23) possible tidal arm, (33) asymmetric disk, (34) possible secondary bulge, (53) partial arms or shells. Image credit: SDSS.

The team of astronomers had expected to find ellipticals (large, mature galaxies) in searching NED, but instead they happened upon this new discovery. This came after sampling around 800,000 galaxies, all within 3.5 billion light-years from the Earth, they found that the most luminous galaxies here not elliptical in shape, but rather spiral.

A distinct trait observed in 4 of the 53 super spirals discovered by the team is that they contain two galactic nuclei, potentially hinting at the origin of such galaxies—a collision of epic proportions.

As the team notes, “double nuclei are a telltale sign of two galaxies having just merged together. Conventionally, mergers of spiral galaxies are destined to become bloated, elliptical galaxies,” but the merging of two gas-rich galaxies could possibly lead to their combined gases settling into a super spiral.

This discovery changes conventional understanding of how massive galaxies form and evolve. Their study is published in the Astrophysical Journal.