A Ring Galaxy

AM 0644-741The blue ring of young stars around the nucleus of AM 0644-741 is 150,000 light-years in diameter, making it larger than our entire galaxy, the Milky Way. Ring galaxies are one example of how collisions between galaxies can produce an significant change in one galaxies structure. One may result from a collision in which an intruder galaxy plunges directly through the disk of a target galaxy. In the case of AM 0644-741, the galaxy that pierced through the ring galaxy is out of the frame of this Hubble image but can be seen in larger-field images. The resulting gravitational shock caused by the collision drastically alters the orbits of stars and gas in the target galaxy’s disk, causing them to rush outward. As that wave spreads out, gas clouds collide and are compressed. The dense clouds contract under their own gravity, collapse, and new stars form.

Image Credit: NASA

The Southern Crab

He2-104An unlikely pair of stars may have created this oddly-shaped nebula resembling nesting hourglasses. Images taken with Earth-based telescopes show the larger, hourglass-shaped nebula, but the Hubble telescope, reveals a smaller nebula embedded in the center of the larger one. See the insert The entire nebula is called the “Southern Crab Nebula” (He2-104) because it looks like the body and legs of a crab as seen from ground-based observatories. The likely source of the the larger and smaller nebulae is a pair of aging stars buried in the glow of the tiny, central nebula. One of them is a red giant, a bloated star that is exhausting its nuclear fuel and is shedding its outer layers in a powerful stellar wind. Its companion is a hot, white dwarf, a stellar zombie of a burned-out star.

Image Credit: NASA

Hercules A

Hercules AHercules A, also known as 3C 348, lies around two billion light-years away. It is one of the brightest sources of radio emission outside our Galaxy. It’s the bright object at the middle of the frame, an elliptical galaxy. As seen in visible light by the Hubble Space Telescope it appears floating serenely in the inky blackness of space, but adding data from a radio telescope radically transforms the image. Jets of material can be seen billowing outwards from the galaxy when viewed at radio frequencies—jets that are completely undetectable in visible light. The image above combines data from the Very Large Array radio observatory in New Mexico with data from Hubble‘s Wide Field Camera 3.

The two jets are composed of hot, high-energy plasma that has been flung from Hercules A by a supermassive black hole lurking at the galaxy’s core. This black hole is roughly 2.5 billion times the mass of the Sun. That’s about a thousand times more massive than the black hole at the centre of the Milky Way.

Hercules A’s black hole accelerates the ejected material to nearly the speed of light, sending it flying out into intergalactic space. Eventually, the highly focused jets lose energy, slowing down and spreading out to form cloud-like blobs The multiple bright rings and knots seen within these blobs suggest that the black hole has sent out successive bursts of material. The jets stretch for around 1.5 million light-years, around 15 times the size of the Milky Way.

Image Credit: NASA / ESA / VLA


A Lonely Galaxy

The loneliest of galaxiesMCG+01-02-015’s unsentimental naming befits its position within the cosmos: it is a void galaxy, located in an almost empty gap between local groups of galaxies. If our galaxy, the Milky Way, were as isolated, we would not even have known of the existence of other galaxies until the development of strong telescopes and detectors in the 1960s. (Instead, some of our neighboring galaxies such as Andromeda and the Magellanic Clouds can be seen by the naked eye.)

BTW, those three bright stars with the cross-shaped diffraction spikes are in the foreground. They’re near by in the Milky Way.

Image Credit: NASA

A Bipolar Nebula

PN Hb 12A bipolar nebula, such as PN Hb 12 shown here, is not one that is off its meds. It’s a distinctive type of nebular formation characterized by an axially symmetric bi-lobed appearance.

The exact cause of this nebular structure is not known, it may be related to a physical process in which a star ejects highly energetic streams of outflow along both poles which may then collide with material surrounding the star, perhaps stellar dust or shells of matter thrown off in a prior supernova event.

Image Credit: NASA