Hubble measures content of the leading arm of the Magellanic Stream: This is a mosaic image of an edge-on view of the Milky Way galaxy, looking toward the central bulge. Superimposed on it are radio-telescope images, coloured pink, of the stretched, arc-shaped Magellanic Stream below the plane of the galaxy and the shredded, fragmented Leading Arm crossing the galaxy’s plane and extending above it. These gas clouds are being gravitationally pulled apart like taffy from the Small and Large Magellanic Clouds — satellite galaxies to our Milky Way — which appear as bright clumps within the gas. The source of the ribbon-like Magellanic Stream was uncovered by the NASA/ESA Hubble Space Telescope about five years ago, and it was found to come from both Magellanic Clouds. However, the source of the Leading Arm remained a mystery until today. Now, scientists have used Hubble’s ultraviolet capabilities to chemically analyse the gas in the Leading Arm and determine its origin. Because they could not directly sample it, they instead used the light from seven quasars — the bright cores of distant active galaxies — to measure how it filtered through the Leading Arm’s gas. These quasars reside billions of light-years beyond the Leading Arm and act as “lighthouses” shining through the gas. Scientists looked for the absorption of the quasars’ ultraviolet light by oxygen in the cloud. This is a good indication of how many heavier elements reside in the Leading Arm’s gas. The team then compared Hubble’s measurements to hydrogen measurements made by the Robert C. Byrd Green Bank Telescope in Green Bank, as well as several other radio telescopes. Marked locations indicate the three brightest of the seven quasars used to study the composition of the Leading Arm. Spectra for these three quasars are superimposed at the bottom of the graphic. The vertical axis of each spectrum indicates how much absorption is taking place. The more absorption, the greater the signal strength is. The horizontal axes indicate the velocities of the gas at different points. Blue boxes isolate the velocities unique to the Leading Arm. The oxygen, combined with the hydrogen, provided conclusive chemical fingerprints to match the origin of the Leading Arm’s gas. The team found that the gas matches the contents of the Small Magellanic Cloud.

Name: Milky Way
Type: Milky Way
Category: Galaxies
Release date: 4 April 2018, 11:23
Credit: NASA, ESA, A. Fox (STScI), D. Nidever et al., NRAO/AUI/NSF and A. Mellinger, Leiden-Argentine-Bonn (LAB) Survey, Parkes Observatory, Westerbork Observatory, Arecibo Observatory, and A. Feild (STScI)

SN 2001ig in NGC 7424: Seventeen years ago, astronomers witnessed supernova 2001ig go off 40 million light-years away in the galaxy NGC 7424, in the southern constellation Grus, the Crane. Shortly after SN 2001ig exploded, scientists photographed the supernova with the European Southern Observatory’s Very Large Telescope (VLT) in 2002. Two years later, they followed up with the Gemini South Observatory, which hinted at the presence of a surviving binary companion. As the supernova’s glow faded, scientists focused the NASA/ESA Hubble Space Telescope on that location in 2016. They pinpointed and photographed the surviving companion, which was possible only due to Hubble’s exquisite resolution and ultraviolet sensitivity. Hubble observations of SN 2001ig provide the best evidence yet that some supernovas originate in double-star systems.

Name: SN 2001ig
Type: Milky Way : Star : Evolutionary Stage : Supernova
Category: Stars
Distance: 40 million light years
Release date: 30 April 2018, 17:48
Credit: NASA, ESA, S. Ryder (Australian Astronomical Observatory), and O. Fox (STScI)

Evolution of Type IIb Stripped-Envelope Supernova: This graphic illustrates the scenario for the processes that create a Type IIb stripped-envelope supernova, in which most, but not all, of the hydrogen envelope is lost prior to the primary star’s explosion. The four panels show the interaction between the SN 2001ig progenitor star, which ultimately exploded, and its surviving companion. 1) Two stars orbit each other and draw closer and closer together. 2) The more massive star evolves faster, swelling up to become a red giant. In this late phase of life, it spills most of its hydrogen envelope into the gravitational field of its companion. As the companion siphons off almost all of the doomed star’s hydrogen, it creates an instability in the primary star. 3) The primary star explodes in a supernova. 4) As the supernova’s glow fades, the surviving companion becomes visible to the Hubble Space Telescope. The faint remnant of the supernova, at lower left, continues to evolve but in this case is too faint to be detected by Hubble.

Type: Milky Way : Star : Evolutionary Stage : Supernova
Category: Stars
Release date: 30 April 2018, 14:58
Credit: NASA, ESA, and A. Feild (STScI)

Hubble's view of dazzling globular cluster NGC 6397: This ancient stellar jewelry box, a globular cluster called NGC 6397, glitters with the light from hundreds of thousands of stars. Astronomers used the NASA/ESA Hubble Space Telescope to gauge the cluster’s distance at 7800 light-years away. NGC 6397 is one of the closest globular clusters to Earth. The cluster’s blue stars are near the end of their lives. These stars have used up their hydrogen fuel that makes them shine. Now they are converting helium to energy in their cores, which fuses at a higher temperature and appears blue. The reddish glow is from red giant stars that have consumed their hydrogen fuel and have expanded in size. The myriad small white objects include stars like our Sun. This image is composed of a series of observations taken from July 2004 to June 2005 with Hubble’s Advanced Camera for Surveys. The research team used Hubble’s Wide Field Camera 3 to measure the distance to the cluster.

Name: NGC 6397
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Ara
Distance: 7800 light years
Release date: 11 February 2021, 16:00
Credit: NASA, ESA, and T. Brown and S. Casertano (STScI) Acknowledgement: NASA, ESA, and J. Anderson (STScI)