Starship Asterisk*

Image Ctredit: ESO/Malesani et al., The Stargate Collaboration

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The circled spot in this Picture of the Week has almost disappeared. What happened? This sequence of images, taken in optical light with ESO’s Very Large Telescope (VLT), shows the gamma-ray burst GRB 221009A fading away. Gamma-ray bursts (GRBs) are the most luminous phenomena that we know of in the universe, and GRB 221009A is the brightest one yet as seen from Earth.

The burst was detected in October 2022 by several gamma-ray space telescopes, such as NASA's Swift and Fermi and ESA’s INTEGRAL. Then, a few hours after the initial detection, ESO’s X-shooter instrument at the VLT took a spectrum, which provided the first distance measurement to the explosion of approximately 2400 million light years. Thanks to this distance measurement, a team of astronomers led by Daniele Bjørn Malesani ... ruled out an origin in the Milky Way, although the burst is still much closer to us than typical GRBs.

The distance also allowed the team to compute the intrinsic luminosity of the explosion. Despite being in our cosmic backyard, the burst is still intrinsically very luminous. It is in fact the most intense GRB for which we could measure its luminosity, and the brightest ever as seen from Earth in the 55 years since the first gamma-ray satellites were put in orbit. According to Malesani’s team, a burst so energetic and so close as this one should probably be observable once every 1000 years.

A team led by Andrew Levan ... observed this unique explosion with JWST at longer wavelengths. Combining the X-shooter spectrum with the JWST data allows for an in-depth investigation of the nature of this unique event. ...

• arXiv > astro-ph > arXiv:2302.07891 > 15 Feb 2023

• arXiv > astro-ph > arXiv:2302.07761 > 15 Feb 2023 (v1), 22 Mar 2023 (v2)

CTIO/NOIRLab/NSF/AURA/T. Slovinský & P. Horálek (IoP Opava)

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From the high altitude of Cerro Tololo Inter-American Observatory (CTIO) in Chile, two astrophotographers captured the elusive sunset phenomenon known as the green flash. This stunning trick of light occurs at sunset and sunrise when light from the Sun travels through the thickest part of Earth’s atmosphere. Acting like a prism, Earth's atmosphere bends, or refracts, the light and separates it into its component wavelengths. Blue and violet light are scattered by the atmosphere, while red, orange and yellow are refracted below the solar disk below the horizon, leaving the green light the most visible during the few seconds that the Sun disappears below the horizon.

Here, though, is another uncommon phenomenon. Distinct thermal layers above the Pacific Ocean led to a Fata Morgana mirage displaying several green flashes. Two photographers from the recent NOIRLab 2022 Photo Expedition jointly worked the controls of the camera to quickly capture the elusive phenomenon.

This image was the NASA Astronomy Picture of the Day on 28 March 2023.

Powerful near-infrared imager will support multi-messenger astronomy research

Globular Cluster Omega Centauri ~ Credit: CTIO/NOIRLab/DOE/NSF/AURA, T.A.
Rector (Univ of Alaska Anchorage/NOIRLab), M. Zamani & D. de Martin (NOIRLab)

NEWFIRM, a high-resolution, near-infrared imager with a wide field of view, has completed its commissioning run on the Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory (CTIO) in Chile, a Program of NSF's NOIRLab. During its commissioning and capabilities testing, astronomers used NEWFIRM to capture a detailed image of the Omega Centauri globular cluster.

At about 17,000 light-years from Earth in the direction of the constellation Centaurus, Omega Centauri is the largest globular cluster in the Milky Way, containing approximately 10 million stars, making it a popular target for observations.

This observing run marks NEWFIRM’s second tenure at CTIO. Prior to returning to Chile, NEWFIRM was installed on the Nicholas U. Mayall Telescope at Kitt Peak National Observatory (KPNO) in Arizona, also a Program of NOIRLab, for observing runs in 2006–2010 and 2012–2016. It was previously installed on the Blanco telescope in 2010–2011.

Prior to re-installation, NEWFIRM was upgraded with new software, control hardware, guiders, computers, and interfaces, thanks to a competitive NSF grant in support of projects promoting multi-messenger astronomy. ...

Many small galaxies are scattered on a black background: mainly, white, oval-shaped and red, spiral galaxies. To the lower right is a galaxy cluster, with a very large and bright elliptical galaxy at its centre. Thin, reddish, stretched-out arcs surround it. One arc is thick and much brighter. Another red galaxy is large and warped, just next to the cluster core.

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Credit: ESA/Webb, NASA & CSA, J. Rigby

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Streaks of light and bright arcs betray the presence of a vast gravitational lens in this image from the NASA/ESA/CSA James Webb Space Telescope. A galaxy cluster in the foreground has magnified distant galaxies, warping their shapes and creating the bright smears of light spread throughout this image. This effect, referred to by astronomers as gravitational lensing, occurs when a massive celestial object such as a galaxy cluster causes a sufficient curvature of spacetime for light to be visibly bent around it, as if by a gargantuan lens.

One of the consequential effects of gravitational lensing is that it can magnify distant astronomical objects, letting astronomers study objects that would otherwise be too faint or far away. This useful quirk of gravitational lensing has also been used to reveal some of the most distant galaxies humanity has ever encountered. The long, bright, and distorted arc spreading out near the core is one such example. A distant galaxy known as the Cosmic Seahorse, its brightness is greatly magnified by the gravitational lens, which has enabled astronomers to study star formation there.

This image was captured by NIRCam, Webb’s primary near-infrared camera, and contains the lensing galaxy cluster SDSS J1226+2149. It lies at a distance of around 6.3 billion light-years from Earth, in the constellation Coma Berenices. By combining Webb’s sensitivity with the magnifying effect of gravitational lensing, astronomers were able to use this gravitational lens to explore the earliest stages of star formation in distant galaxies. To do so, they relied on earlier studies by the NASA/ESA Hubble Space Telescope, which provided the ‘prescription’ for this gravitational lens.

This image shows only one observation from a programme designed to probe star formation in distant galaxies. As well as revealing how quickly stars form and characterising the environments in these galaxies that gave rise to new stars, these observations will demonstrate the capabilities of Webb and provide richly detailed datasets to the astronomical community. Astronomers expect Webb’s crystal-clear vision and cutting-edge instruments to provide new insights into star formation in distant, gravitationally lensed galaxies.

A spiral galaxy. It has two almost-straight arms coming from the left and right of the core that meet a starry ring around the galaxy’s edge. The ring is bluish in colour, and the core is golden and shining. A faint halo of light also surrounds the galaxy. There is one bright star with many diffraction spikes, and a few small stars all around on a black background.

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Credit: ESA/Hubble & NASA, A. Barth, R. Mushotzky

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This luminous Picture of the Week shows Z 229-15 — imaged here in beautiful detail by the NASA/ESA Hubble Space Telescope — a celestial object that lies about 390 million light-years from Earth in the constellation Lyra. Z 229-15 is one of those interesting celestial objects that, should you choose to research it, you will find defined as several different things: sometimes as an active galactic nucleus (an AGN); sometimes as a quasar; and sometimes as a Seyfert galaxy. Which of these is Z 229-15 really? The answer is that it is all of these things all at once, because these three definitions have significant overlap.

AGNs and quasars are both described in detail in the Hubble Word Bank, but in essence an AGN is a small region at the heart of certain galaxies (called active galaxies) that is far brighter than just the galaxy’s stars would be. The extra luminosity is due to the presence of a supermassive black hole at the galaxy’s core. Material sucked into a black hole actually doesn’t fall directly into it, but instead is drawn into a swirling disc, from where it is inexorably tugged towards the black hole. This disc of matter gets so hot that it releases a large amount of energy across the electromagnetic spectrum, and that’s what makes AGNs appear so bright.

Quasars are a particular type of AGN; they are typically both extremely bright and extremely distant from Earth — several hundred million light-years is considered nearby for a quasar, making Z 229-15 positively local. Often an AGN is so bright that the rest of the galaxy cannot be seen, but Seyfert galaxies are active galaxies that host very bright AGNs (quasars) while the rest of the galaxy is still observable. So Z 229-15 is a Seyfert galaxy that contains a quasar, and that, by definition, hosts an AGN. Classification in astronomy can be a challenge!

A thin spiral galaxy is seen edge-on in the lower right. Its bulge and arms are very bright, mixing reddish and bluish light. Patchy blue trails extend below it, resembling tentacles, made from star-forming regions. Six small, reddish elliptical galaxies are scattered. A very large elliptical galaxy with two cores sits by the top of the frame.

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Image Credit: ESA/Hubble & NASA, M. Gullieuszik and the GASP team

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The galaxy JW100 features prominently in this image from the NASA/ESA Hubble Space Telescope, with streams of star-forming gas dripping from the disc of the galaxy like streaks of fresh paint. These tendrils of bright gas are formed by a process called ram pressure stripping, and their resemblance to dangling tentacles has led astronomers to refer to JW100 as a ‘jellyfish’ galaxy. It is located in the constellation Pegasus, over 800 million light-years away.

Ram pressure stripping occurs when galaxies encounter the diffuse gas that pervades galaxy clusters. As galaxies plough through this tenuous gas it acts like a headwind, stripping gas and dust from the galaxy and creating the trailing streamers that prominently adorn JW100. The bright elliptical patches in the image are other galaxies in the cluster that hosts JW100.

As well as JW100’s bright tendrils, this image also contains a remarkably bright area of diffuse light towards the top of this image which contains two bright blotches at its core. This is the core of IC 5338, the brightest galaxy in the galaxy cluster, known as a cD galaxy. It’s not unusual for cD galaxies to exhibit multiple nuclei, as they are thought to grow by consuming smaller galaxies, the nuclei of which can take a long time to be absorbed. The bright points of light studding its outer fringes are a rich population of globular clusters.

This observation took advantage of the capabilities of Hubble’s Wide Field Camera 3 (WFC3), and is part of a sequence of observations designed to explore star formation in the tendrils of jellyfish galaxies. These tendrils represent star formation under extreme conditions, and could help astronomers understand the process of star formation elsewhere in the universe.

• Astrophysical Journal 945(1):54 (2023 Mar 01) DOI: 10.3847/1538-4357/acb59b
• arXiv > astro-ph > arXiv:2301.08279 > 19 Jan 2023

• arXiv > astro-ph > arXiv:2302.10615 > 21 Feb 2023

Image Credit: ESO/A. Ghizzi Panizza (albertoghizzipanizza.com)

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This Picture of the Week shows a beautiful meeting between the Swedish–ESO Submillimetre Telescope (SEST) and the Milky Way, apparently almost touching each other. This shot was taken at ESO’s La Silla Observatory, located on the outskirts of the Chilean Atacama Desert, at an altitude of 2400 metres.

Light and darkness shape the Milky Way as it stretches across the night sky. The dark patches are dust clouds blocking the light behind them, coming from millions of stars in the central region of our galaxy.

SEST was built on behalf of the Swedish Natural Science Research Council (NFR) and ESO in 1987. It is a 15-m radio telescope, and it was the only large sub-millimetre telescope in the southern hemisphere at the time of first light. In 2003, the telescope was decommissioned as it was superseded by the Atacama Pathfinder EXperiment telescope (APEX) and the Atacama Large Millimeter / submillimeter Array (ALMA) further north in Chile. Over the years SEST has observed a wide range of astronomical objects, from comets to stellar nurseries and galaxies.

Image Credit: KPNO/NOIRLab/NSF/AURA

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The nebula that keeps on giving, Messier 1 (Crab Nebula) is captured here by the Nicholas U. Mayall 4-meter Telescope from Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab. The storied history of this supernova remnant in modern astronomy begins when it was recorded in 1731 by British astronomer John Bevis, who believed it was nothing more than a cloudy blob. It was more than three decades later that French comet hunter Charles Messier clarified that the object was in fact something, and it became the first entry in his catalog of nebulae and star clusters. Then in the early 20th century astronomers connected Messier 1 to a supernova explosion observed by Chinese astronomers in 1054. This made the Crab Nebula the first astronomical object to be connected to a previously observed supernova.

A pulsar — the ultra-dense, rapidly spinning remnant of a star — inside the Crab Nebula was discovered in 1968 at radio wavelengths. Its presence in the optical part of the spectrum was confirmed a year later by Americans John Cocke and Donald Taylor and British astronomer Michael Disney using the UArizona 0.9-meter Spacewatch Telescope at KPNO. The Crab Pulsar then became integral in advancing scientific understanding of supernova remnants: it was the first of its kind to link a historical supernova to a pulsar whose precise age is known.

This image was the last taken with the Mayall telescope before the Dark Energy Spectroscopic Instrument (DESI) was installed. The Crab Nebula was also the first target for the telescope’s first light in 1973.

A wide band of bluish light extends from the centre of the image to the right side. It is speckled with many tiny stars, and a few small, bright red bubbles of gas, identifying it as a galaxy. The background is black, and has small galaxies and stars spread around. Most are too small to distinguish, except for two oval-shaped galaxies, each having a hazy glow around a bright centre. Image Credit: ESA/Hubble & NASA, R. Tully

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UGCA 307 hangs against an irregular backdrop of distant galaxies in this image from the NASA/ESA Hubble Space Telescope. The small galaxy consists of a diffuse band of stars containing red bubbles of gas that mark regions of recent star formation, and lies roughly 26 million light-years from Earth in the constellation Corvus. Appearing as just a small patch of stars, UGCA 307 is a diminutive dwarf galaxy without a defined structure — resembling nothing more than a hazy patch of passing cloud.

This image is part of a Hubble project to explore every known nearby galaxy, giving astronomers insights into our galactic neighbourhood. Before this set of observations, almost three quarters of nearby galaxies had been investigated by Hubble in enough detail to spot the brightest stars and build up an understanding of the stars populating each galaxy. This Hubble project set out to explore the remaining quarter of nearby galaxies by taking advantage of short gaps in Hubble’s observing schedule.

This crystal-clear image was captured by Hubble’s Advanced Camera for Surveys (ACS), which was installed on the telescope in 2002 during Servicing Mission 3B. Hubble’s vantage point in low Earth orbit means that it is above atmospheric turbulence, giving it a sharper view of the Universe. However, it is also close enough to Earth that astronauts could visit the telescope to repair and refurbish the telescope. In total, five Space Shuttle missions flew to Hubble and kept it at the forefront of astronomy by installing new instruments. The ACS replaced one of Hubble’s original instruments, the Faint Object Camera, which was built by ESA.

Credit:D. López Calvin (solarigrafia.com), J. C. Muñoz Mateos / ESO. CC-BY-NC 4.0

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This picture of the week shows the Sun’s path on the sky as seen from ESO’s Paranal Observatory in Chile. The picture was taken with a pinhole camera with an exposure of 8 months, from 17 April to 11 December 2018. The tall structure in the foreground is the “seeing monitor”, which measures the blur/twinkling of the stars due to the atmospheric turbulence. In the background we can see several domes; the ones to the centre-left are part of the Very Large Telescope, and the rightmost one is the VLT Survey Telescope.

But what are those bright coloured lines behind them? They are created by the Sun as it moves in the sky throughout the day, leaving an imprint on the sheet of photographic paper placed inside the pinhole camera.

The camera was facing west, so here we see hundreds of sunsets. But as the Earth moves around the Sun, each day the Sun sets at a different point along the horizon. The shortest arc all the way to the right of the image corresponds to the winter solstice (June 21 in the Southern Hemisphere), when the Sun reaches its lowest elevation. From that point onwards, the Sun moves southward day after day, to the left in this image. The arcs become longer and higher, and the days longer and hotter. Then, on the summer solstice (December 21), the Sun reaches its highest point, which is not visible in this picture, and draws the longest arc to the left of this image.

The dark lines are due to clouds blocking the Sun. Luckily for astronomers, Paranal Observatory boasts over 300 clear days per year, hence the very few dark bands in this image.

bystander wrote: ↑Mon Mar 06, 2023 3:10 pm Plunge into a Stellar Ocean
ESO Picture of the Week | 2023 Mar 06

potw2310a[1].jpgCredit: ESO/VPHAS+ team. Acknowledgement: Cambridge Astronomical Survey Unit

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In this Picture of the Week, we take a deep plunge into the ocean of stars in the IC4701 nebula. This nebula is located in the Sagittarius constellation, and it is twice as wide as the full Moon in the sky. The energetic light from newly-born stars ionizes the hydrogen gas in the nebula, causing it to emit the intense reddish hue seen in this picture. The dark clouds in this image contain large amounts of interstellar dust, too dense for the light of the background stars to pierce through it.

The IC4701 nebula is part of a rich and vast complex of dust and gas within which new stars spring to life. When stars are born, most of them are cooler, redder, and less massive than our own Sun. Hotter, more massive stars are much rarer, and they quickly burn through all their fuel and die. This makes these brilliant blue and massive stars, and their surrounding glowing gas, beacons of recent star formation.

Image Credit: International Gemini Observatory/NOIRLab/NSF/AURA/J. Chu

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Maunakea, the huge volcano in the background of this image, is one of the five volcanoes on the island of Hawai‘i. Maunakea is home to a number of astronomical observatories, including Gemini North, one half of the International Gemini Observatory, operated by NSF’s NOIRLab.

It may not look like it, but this image was taken at night, not on a sunny afternoon as it might appear at first glance. The Moon reflects sunlight rather evenly across the visible spectrum, albeit at a brightness of only 0.3 lux — about 300,000 times fainter than the Sun. With a long exposure, moonlight can appear to illuminate scenery just as though it were a sunny day. If you look closely you might notice a few stars visible in the sky.