Every year, in celebration of another monumental anniversary of observations and discovery,
the astronomers operating the Hubble Space Telescope release an annual image highlighting
the beauty of our cosmos.
This year, in March of 2019, Hubble took aim at the southern hemisphere and stared for
52 minutes using several filters at a spot in the sky only 1.4 arcminutes across.
And there, hidden in the constellation Centaurus and high in the sky lies the southern Crab
Nebula.
This nebula is located 10,700 light years away and spans almost 4.4 light years across.
Using several filters on the Wide Field Camera 3 onboard Hubble, vibrant colors and an hourglass
shape resembling the legs of a crab are easily seen.
These two nested hourglass-shaped structures are thought to be sculpted by a whirling pair
of stars in a binary system embedded deep in the gas and dust surrounding them.
Astronomers think the two stars embedded within consists of an aging red giant star and a
burned-out star, a white dwarf.
The red giant is shedding its outer layers and some of this ejected material is attracted
by the gravity of the companion white dwarf.
The bubbles of gas and dust appear brightest at the edges, giving the illusion of crab
leg structures.
These "legs" are likely to be places where the outflow slams into surrounding interstellar
gas and dust, it may also be material which was earlier lost by the red giant star.
This 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.
In order to learn what chemicals are in the nebula, Hubble observed a cross section of
the gas using the onboard Space Telescope Imaging Spectrograph (or STIS).
Inside this narrow window, light was divided into a spectrum of colors.
By doing this, the specific glow from hydrogen, sulfur, oxygen, and nitrogen could be isolated.
Once injected into interstellar space, these elements will be available for future generations
of stars, planets, and possibly life.
The Hubble Space Telescope has been observing the heavens for 29 years and shows no signs
of slowing down.
No other instrument has shown us more and provided more context than the images sent
by this venerable telescope.