A Hermit Galaxy

UGC 4879 is an irregular dwarf galaxy. It is very isolated, which means that it has not interacted with any surrounding galaxies, making it an ideal laboratory for studying star formation uncomplicated such interactions. Studies of UGC 4879 have revealed a significant amount of star formation in the first 4-billion-years after the Big Bang, followed by a strange nine-billion-year lull in star formation which ended about 1-billion-years ago. That behavior is puzzling, and the solitary galaxy continues to provide ample study material for astronomers looking to understand the complex mysteries of starbirth throughout the Universe.

Image Credit: ESA / NASA

The Heart of the Crab

The supernova explosion that formed the Crab Nebula was first seen on Earth in the year 1054. In 2000, astronomers released this image of the still-evolving center of the explosion. The composite photograph was taken in colors emitted by specific elements including hydrogen (orange), nitrogen (red), sulfur (pink), and oxygen (green). The result looks a lot like a Jackson Pollock painting. The complex array of gas filaments are rushing out from the explosion at over 5,000,000 km/h. Even at that tremendous speed, it takes over 600 years to cross the 3 light year wide frame of this picture.

The rapidly spinning neutron star remnant of supernova is visible as the lower of the two bright stars near the center of the image. The Crab Nebula (aka M1) is about 6,500 light-years away in the direction the constellation of Taurus.

Image Credit: NASA

The Helix Nebula

helixnebulaThis infrared image taken by the Spitzer Space Telescope looks a bit like Sauron’s eye. It’s the Helix Nebula, a cosmic site often photographed by amateur astronomers because of its vivid colors and eerie resemblance to a giant eye. It’s about 700 light-years away in the constellation Aquarius and belongs to a class of objects called planetary nebulae.

Planetary nebulae are the remains of stars that were once like our Sun. When these stars die, they puff out their outer gaseous layers which are heated by the hot core of the dead star. The remnant becomes a white dwarf and shines with infrared and visible light. Our Sun probably will expand into a planetary nebula in around five billion years.

Spitzer‘s infrared view of the Helix nebula shows the outer gaseous layers is in blues and greens. The red color in the middle of the eye is the final layers of gas blown out when the star died. Blue shows infrared light of 3.6 to 4.5 µm wavelengths, green shows infrared light of 5.8 to 8 µm, and red shows infrared light of 24 µm.

The brighter red circle in the very center is the glow of the dust circling the white dwarf. This dust is thought to have been kicked up by comets that survived the death of the original star. Before the star died, its comets and possibly planets would have orbited the star in an orderly fashion. But when the star blew off its outer layers, it’s inner planets would have been swallowed up in its expanding shell, but the icy bodies and outer planets would have been stirred up and into tossed into each other, creating a cosmic dust storm. The Helix nebula is one of only a few dead-star systems in which evidence for cometary survivors has been found.

Image Credit: NASA