In celebration of the 29th anniversary of the launch of the NASA/ESA Hubble Space Telescope, astronomers captured this colorful look at the hourglass-shaped Southern Crab Nebula.
This incredible image of the Southern Crab Nebula was taken to mark Hubble’s 29th anniversary in space. Image credit: NASA / ESA / STScI.
On April 24, 1990, Hubble was launched on the space shuttle Discovery. It has since revolutionized how astronomers and the general public see the Universe. The images it provides are spectacular from both a scientific and a purely aesthetic point of view.
Each year the telescope dedicates a small portion of its precious observing time to take a special anniversary image, focused on capturing particularly beautiful and meaningful objects. This year’s image is the Southern Crab Nebula, and it is no exception.
The Southern Crab Nebula resides in the southern constellation Centaurus, approximately 7,000 light-years from Earth. It is so named to distinguish it from the better-known Crab Nebula, a supernova remnant visible in the constellation of Taurus.
The prosaic name of this nebula is Hen 2-104, meaning that it was first catalogued as number 104 in the second list of emission-line stars, compiled by the American astronomer-astronaut Karl Henize in 1967.
The object appears to have two nested hourglass-shaped structures that were sculpted by a whirling pair of stars in a binary system. The duo consists of an aging red giant star and a white dwarf. The red giant is shedding its outer layers. Some of this ejected material is attracted by the gravity of the companion white dwarf.
The result is that both stars are embedded in a flat disk of gas stretching between them. This belt of material constricts the outflow of gas so that it only speeds away above and below the disk.
The bubbles of gas and dust appear brightest at the edges, giving the illusion of ‘crab leg’ structures. These ‘legs’ are likely to be the places where the outflow slams into surrounding interstellar gas and dust, or possibly material which was earlier lost by the red giant star.
The outflow may only last a few thousand years, a tiny fraction of the lifetime of the system. This means that the outer structure may be just thousands of years old, but the inner hourglass must be a more recent outflow event.
The red giant will ultimately collapse to become a white dwarf. After that, the surviving pair of white dwarfs will illuminate a shell of gas called a planetary nebula.
The Southern Crab Nebula was assumed to be an ordinary star until 1989, when it was observed using telescopes at ESO’s La Silla Observatory.
The resulting image showed a roughly crab-shaped extended nebula, formed by symmetrical bubbles of gas and dust. Those observations only showed the outer hourglass emanating from a bright central region that could not be resolved.
It was not until Hubble observed the nebula in 1999 that the entire structure came into view. That image revealed the inner nested structures, suggesting that the phenomenon that created the outer bubbles had occurred twice in the recent past.
It is fitting that Hubble has returned to this object twenty years after its first observation. The new image adds to the story of an active and evolving object and contributes to the story of Hubble’s role in our evolving understanding of the Universe.
