Happy Birthday Hubble

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.

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.

This incredible image of the Southern Crab Nebula was taken to mark Hubble’s 29th anniversary in space. Image credit: NASA / ESA / STScI.

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 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 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 seems 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.

The Milky Way is Really Big

The Milky Way Galaxy (the one we’re in) contains an estimated 200 billion stars. But that’s just the tip of the iceberg, the Galaxy is surrounded by vast amounts of an unknown material called “dark matter” (matter that we can’t normally detect because it doesn’t interact with the electromagnetic spectrum). Astronomers know it exists because, dynamically, the Milky Way would fly apart if dark matter didn’t keep a gravitational lid on things.

Image result for milky way galaxy

You are here

Still, astronomers would like to have a more precise measure of the Galaxy’s total mass to better understand how the myriad galaxies throughout the Universe form and evolve. A team of researchers from ESO, the Space Telescope Science Institute, the Johns Hopkins University Center for Astrophysical Sciences, and the University of Cambridge combined observations from the NASA/ESA Hubble Space Telescope and ESA’s Gaia satellite to study the motions of globular star clusters that orbit our Galaxy. The faster the clusters move under the entire Galaxy’s gravitational pull, the more massive it is. The team concluded the Milky Way has an equivalent mass of 1.54 trillion solar masses, most of it locked up in dark matter.

This new mass estimate puts the Milky Way Galaxy on the beefier side, compared to other galaxies in the Universe. The lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion, or 30,000 times more massive. The Milky Way’s mass of 1.5 trillion solar masses is fairly normal for a galaxy of its brightness.

Previous estimates of the Milky Way’s mass ranged from 500 billion to 3 trillion solar masses. This huge margin of error arose primarily from the different methods used for measuring the distribution of dark matter, which makes up about 90% of the mass of the Galaxy.

Given the elusive nature of the dark matter, the team had to use a clever method to weigh the Milky Way, which relied on measuring the velocities of globular clusters, dense star clusters that orbit the spiral disk of the Galaxy at great distances.

The scientists used Gaia’s second data release, which includes measurements of globular clusters as far as 65,000 light-years from Earth, as a basis for the study.

Observations from Hubble allowed faint and distant globular clusters, as far as 130,000 light-years from Earth, to be added to the study. As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.

By combining Gaia’s measurements with measurements from Hubble, the scientists could better pin down the Milky Way’s mass in a way that would be impossible without both space telescopes,

The team’s results will be published in the Astrophysical Journal.