Hubble Captures NGC 4698, an Out of Sync Galaxy Spinning Two Ways at Once

Hubble’s new frame of NGC 4698 arrives from 55 million light years out in Virgo, a spiral tucked into the nearest big cluster of more than a thousand galaxies bound by gravity. Brown dust lanes cut through the outer disk and young blue stars light the same curves, yet those arms refuse to spiral into the middle. They hang in a ring around the perimeter and leave the bright core standing on its own, with reddish pockets of fresh star birth mixed among the dust.

Pale older stars form a vast bulge with a faint off-white tint that spins around a monster black hole several million times heavier than our sun, and this black hole just keeps feeding, growing larger with each passing instant, dining on gas that is pulled in. The bulge is perched at a 90-degree angle to the disk, so a delicate thread of faint starlight can be seen peeking up and down from the dusty plane. The stars and gas closest to the center behave strangely, moving in straight lines at a right angle to the outer ring, so there is no overlap between the inner stars and the outer disk because they spin in different directions.

It is now assumed that some of the gas that strayed in from outside developed its own inner disk with a different angle from the one we see now, and that a short hydrogen tail on one side represents the ghost of a minor galaxy that NGC 4698 swallowed up a long time ago. Hubble captured this light with the Wide Field Camera 3 as part of program 18103, which was led by D. Thilker and the MAUVE-HST team. They used ultraviolet to red filters, as well as a unique line, to map out star clusters and nebulae across the Virgo Cluster. This same set of data provides some unique insights into how a galaxy’s journey through a crowded neighborhood can either impede or reshape any new star formation that occurs.

NGC 4698 is one of a small number of spirals in which the inner stars ignore the spin of the outer disk and go on anyway, and this Hubble image shows that mismatch in a single glimpse, from the quieter ring of blue stars to the sideways brightness in the center.