Starship Asterisk*

bystander wrote: ↑Mon Jul 31, 2023 4:16 pm NGC 6652
ESA Hubble Picture of the Week | 2023 Jul 31

Click to view full size image

A dense spherical cluster of stars. The stars merge into a bright core in the centre,
and spread out to the edges gradually, giving way to an empty, dark background.
Most of the stars are small points of light. A few stars with cross-shaped diffraction
spikes appear larger, and stand out in front.
(Credit: ESA/Hubble & NASA, A. Sarajedini, G. Piotto)

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The glittering, glitzy contents of the globular cluster NGC 6652 sparkle in this star-studded image from the NASA/ESA Hubble Space Telescope. The core of the cluster is suffused with the pale blue light of countless stars, and a handful of particularly bright foreground stars are adorned with criss-crossing diffraction spikes. NGC 6652 lies in our own Milky Way galaxy in the constellation Sagittarius, just under 30 000 light-years from Earth and only 6500 light-years from the Galactic centre.

Globular clusters are stable, tightly gravitationally bound clusters containing anywhere between tens of thousands and millions of stars. The intense gravitational attraction between the closely packed stars in globular clusters is what gives these star-studded objects their regular, spherical shape.

This image combines data from two of Hubble’s third-generation instruments; the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). As well as two instruments, this image draws on two different observing programmes from two different teams of astronomers. The first team set out to survey globular clusters in the Milky Way galaxy in the hope of shedding light on topics ranging from the ages of these objects to the gravitational potential of the galaxy as a whole. The second team of astronomers used a trio of exquisitely sensitive filters in Hubble’s Wide Field Camera 3 to disentangle the proportions of carbon, nitrogen, and oxygen in globular clusters such as NGC 6652.

A dense field of stars with clouds of gas and dust billowing across it. The clouds are patchy and wispy, dense and glowing parts obscuring the centre of the image. Bright galaxies with various shapes and sizes shine through the gas and stars. Some of the star images are a bit larger than the rest, with visible diffraction spikes; two foreground stars are bright in the lower-right corner. (Image Credit: ESA/Webb, NASA & CSA, M. Meixner)

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Click to view full size image 1 or image 2

NGC 6822 (MIRI / NIRCam image)

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This image shows the irregular galaxy NGC 6822, which was observed by the Near-InfraRed Camera (NIRCam) and Mid-InfraRed Instrument (MIRI) mounted on the NASA/ESA/CSA James Webb Space Telescope. As their names suggest, NIRCam and MIRI probe different parts of the electromagnetic spectrum. This allows the instruments to observe different components of the same galaxy, with MIRI especially sensitive to its gas-rich regions (the yellow swirls in this image) and NIRCam suitable for observing its densely packed field of stars.

NGC 6822 lies about 1.5 million light-years away, and is the Milky Way’s nearest galactic neighbour that is not one of its satellites. It has a low metallicity, meaning that it contains low proportions of elements that are not hydrogen and helium. Metallicity is an absolutely key concept in astronomy, in part because elements other than hydrogen and helium are largely produced by stars over their lifetimes. Therefore, in the very early Universe (before the first generation of stars had been born, lived and died) everything had very low metallicity. This makes contemporary low-metallicity objects (like NGC 6822) objects of interest for understanding how processes such as the evolution of stars and the life cycle of interstellar dust likely occurred in the early Universe. This was the motivation for these observations of NGC 6822 with Webb: to better understand how stars form and how dust evolves in low-metallicity environments.

The study of NGC 6822 has an interesting history that long predates modern investigations with Webb. It was first discovered by E. E. Barnard, who presented his discovery in a very brief paper in 1884 in The Sidereal Messenger: a short-lived but important American monthly astronomical journal that was published between 1882 and 1891. As with many astronomical objects that appeared diffuse with telescopes of the time, NGC 6822 was miscategorised as an “exceedingly faint nebula”. ...

A dense spherical cluster of stars. The stars merge into a bright core in the centre,
and spread out to the edges gradually, giving way to an empty, dark background.
Most of the stars are small points of light. A few stars with cross-shaped diffraction
spikes appear larger, and stand out in front.
(Credit: ESA/Hubble & NASA, A. Sarajedini, G. Piotto)

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The glittering, glitzy contents of the globular cluster NGC 6652 sparkle in this star-studded image from the NASA/ESA Hubble Space Telescope. The core of the cluster is suffused with the pale blue light of countless stars, and a handful of particularly bright foreground stars are adorned with criss-crossing diffraction spikes. NGC 6652 lies in our own Milky Way galaxy in the constellation Sagittarius, just under 30 000 light-years from Earth and only 6500 light-years from the Galactic centre.

Globular clusters are stable, tightly gravitationally bound clusters containing anywhere between tens of thousands and millions of stars. The intense gravitational attraction between the closely packed stars in globular clusters is what gives these star-studded objects their regular, spherical shape.

This image combines data from two of Hubble’s third-generation instruments; the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). As well as two instruments, this image draws on two different observing programmes from two different teams of astronomers. The first team set out to survey globular clusters in the Milky Way galaxy in the hope of shedding light on topics ranging from the ages of these objects to the gravitational potential of the galaxy as a whole. The second team of astronomers used a trio of exquisitely sensitive filters in Hubble’s Wide Field Camera 3 to disentangle the proportions of carbon, nitrogen, and oxygen in globular clusters such as NGC 6652.

A broad spiral galaxy seen directly face-on. It has two bright spiral arms that extend from a bar, which shines from the very centre. Additional fainter arms branch off from these, studded with bright blue patches of star formation. Small, distant galaxies are dotted around it, on a dark background. (Credit: ESA/Hubble & NASA, A. Filippenko, J. Lyman)

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The tranquil spiral galaxy UGC 12295 basks leisurely in this image from the NASA/ESA Hubble Space Telescope. This galaxy lies around 192 million light-years away in the constellation Pisces, and is almost face-on when viewed from Earth, displaying a bright central bar and tightly wound spiral arms.

Despite appearing as an island of tranquillity in this image, UGC 12295 played host to a catastrophically violent explosion — a supernova — that was first detected in 2015. This supernova prompted two different teams of astronomers to propose Hubble observations of UGC 12295 that would sift through the wreckage of this vast stellar explosion.

Supernovae are the explosive deaths of massive stars, and are responsible for forging many of the elements found here on Earth. The first team of astronomers used Hubble’s Wide Field Camera 3 (WFC3) to examine the detritus left behind by the supernova in order to better understand the evolution of matter in our Universe.

The second team of astronomers also used WFC3 to explore the aftermath of UGC 12295’s supernova, but their investigation focused on returning to the sites of some of the best-studied nearby supernovae. Hubble’s keen vision can reveal lingering traces of these energetic events, shedding light on the nature of the systems that host supernovae.

An irregular galaxy that appears like a triangle-shaped patch of tiny stars. It is densest in the centre and along one edge, growing faint out to the opposite corner. Several bright pink patches mark areas of star formation, and the galaxy’s brightest stars are around these. A large, bright star, with two sets of long spikes, stands between the viewer and the galaxy. (Image Credit: ESA/Hubble & NASA, J. Dalcanton, A. Filippenko)

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The irregular galaxy Arp 263 lurks in the background of this image from the NASA/ESA Hubble Space Telescope, but the view is dominated by a stellar photobomber; the bright star BD+17 2217. Arp 263 — also known as NGC 3239 — is a patchy, irregular galaxy studded with regions of recent star formation, and astronomers believe that its ragged appearance is due to its having formed from the merger of two galaxies. It lies around 25 million light-years away in the constellation Leo.

Two different Hubble investigations into Arp 263, using two of Hubble’s third-generation instruments, contributed data to this image. The first investigation was part of an effort to observe the sites of recent supernovae, such as the supernova SN 2012A that was detected just over a decade ago in Arp 263. Astronomers used Hubble’s powerful Wide Field Camera 3 (WFC3) to search for lingering remnants of the colossal stellar explosion. The second investigation is part of a campaign using Hubble’s Advanced Camera for Surveys (ACS) to image all the previously unobserved peculiar galaxies in the Arp catalogue, including Arp 263, in order to find promising subjects for further study using the NASA/ESA/CSA James Webb Space Telescope.

The interloping foreground star, BD+17 2217, is adorned with two sets of criss-crossing diffraction spikes. The interaction of light with Hubble’s internal structure means that concentrated bright objects such as stars are surrounded by four prominent spikes. Since this image of BD+17 2217 was created using two sets of Hubble data, the spikes from both images surround this stellar photobomber. The spikes are at different angles because Hubble was at different orientations when it collected the two datasets.

Image Credit: ESO/Meingast et al.

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Can you see the chameleon in this picture? No? Well, it's camouflaged! Yes, we are joking, but this Picture of the Week actually shows the Chamaeleon Cloud, or IC 2631. In the southern hemisphere, this cloud is visible in the sky for most of the year, and in this image, captured by ESO’s Visible and Infrared Survey Telescope for Astronomy (VISTA), you can admire it in infrared light.

IC 2631 is a reflection nebula made of dust clouds that reflect the light emitted from nearby stars. The nebula is mainly illuminated by one of the youngest, most massive and brightest stars in its neighborhood, HD 97300, visible to the centre-right of the image. The Chamaeleon Cloud is in fact the brightest nebula in the Chamaeleon Complex, a vast region of gas and dust clouds –– much larger than what this image shows –– where numerous newborn and still-forming stars live.

The cloud you see here is packed full of star-making material: gas and dust. At optical wavelengths this region contains dark patches where dust completely blocks light from background sources. But this image was captured in infrared light, which can pass through dust almost unimpeded, allowing scientists to peer into the core of this cloud.

• Astronomy & Astrophysics 673:A58 (May 2023) DOI: 10.1051/0004-6361/202245771
• arXiv > astro-ph > arXiv:2303.08831 > 15 Mar 2023

• Astronomy & Astrophysics 673:A59 (May 2023) DOI: 10.1051/0004-6361/202245772
• arXiv > astro-ph > arXiv:2303.08840 > 15 Mar 2023