Galactic Onion

Galactic onionThis is NGC 3923, an example of a shell galaxy in which the stars in its halo are arranged in layers. Roughy ten percent of all elliptical galaxy exhibits this onion-like structure. The shell-like structures are thought to result from galactic cannibalism when a larger galaxy swallows a smaller companion. As the galactic centers approach, they initially oscillate about a common center. Ripples flow outwards forming the shells of stars, a three dimensional equivalent of ripples on a pond spreading across its surface. NGC 3923 has over twenty shells, but only a few of the outer ones visible in this picture.

Image Credit: ESA / NASA

The Oyster Nebula

A hazy nebulaThis is a false color image from Hubble’s Wide Field Planetary Camera 2 of NGC 1501, a complex planetary nebula located in the constellation of Camelopardalis (The Giraffe). NGC 1501 is a planetary nebula that is just under 5,000 light-years away from us. It has a central star shining brightly from within the nebula’s cloud. This bright pearl embedded in its glowing shell gives rise to the nebula’s popular nickname—the Oyster Nebula.

While NGC 1501’s central star blasted off its outer shell long ago, it still remains very hot and luminous, but it can be difficult to spot through modest telescopes. The star seems to be pulsating, varying quite significantly in brightness over a timescale of just half an hour. While variable stars are not unusual, it is unusual to find one at the heart of a planetary nebula.

Image Credit: ESA / NASA

I Zwicky 18

I_Zwicky_18I Zwicky 18 is a dwarf irregular galaxy located about 59 million light years away. Spectroscopic observations with ground-based telescopes showed that I Zwicky 18 to be almost completely made up of hydrogen and helium, the main ingredients created in the Big Bang, and galaxies with I Zwicky 18’s youthful appearance are typically found only in the early universe. Initial observations with the Hubble Space Telescope suggested an age of 500 million years, but later Hubble observations found faint, older stars in the galaxy, suggesting its star formation started at least one billion years ago and possibly as much as ten billion years ago. It’s possible that the galaxy may have formed around the same time as most other galaxies.

Image Credit: NASA / ESA

Happy 25th Birthday, Hubble

This animation provides a 3D perspective on Hubble‘s 25th anniversary image of the nebula Gum 29 and the star cluster Westerlund 2 at its core. It begins fly past foreground stars and approaches the rim of the nebula. After passing through the wispy darker clouds on the near side, the simulation shows the bright gas illuminated by the intense radiation of the new stars forming in the Westerlund 2 cluster. The pillars of dark, dense gas are being sculpted by light and strong stellar winds from thousands of stars. This visualization is intended to be a scientifically reasonable interpretation, but distances within the model have been significantly compressed.

Video Credit: NASA, ESA, G. Bacon, L. Frattare, Z. Levay, and F. Summers (Viz3D Team, STScI), and J. Anderson (STScI)
Acknowledgment: The Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), the Westerlund 2 Science Team, and ESO


The crammed centre of Messier 22This is the center of the globular cluster Messier 22 as seen by the Hubble Space Telescope. Globular clusters are more-or-less spherical collections of densely packed stars; they are relics of the early years of the Universe with ages of in the range of 12 to 13 billion years. The Universe is only 13.8 billion years old.

M22 is one of about 150 globular clusters in the Milky Way, and it is also one of the closest to Earth, only about 10,000 light-years away. The cluster has a diameter of about 70 light-years and appears to take up a patch of sky the size of the full Moon. However, the light from the stars in the cluster is not very bright because it is dimmed by dust and gas between the solar system and the cluster.

M22 in particular has some fascinating features: six planet-sized objects that are not orbiting a star have been detected in the cluster, and it contains two black holes.

Image Credit: ESA/NASA