Starship Asterisk*

Credit: ESA/Hubble & NASA, L.Ferrarese et al.

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Many of the best-loved galaxies in the cosmos are remarkably large, close, massive, bright, or beautiful, often with an unusual or intriguing structure or history. However, it takes all kinds to make a Universe — as demonstrated by this Hubble Picture of the Week of Messier 110.

Messier 110 may not look like much, but it is a fascinating near neighbour of our home galaxy, and an unusual example of its type. It is a member of the Local Group, a gathering of galaxies comprising the Milky Way and a number of the galaxies closest to it. Specifically, Messier 110 is one of the many satellite galaxies encircling the Andromeda Galaxy, the nearest major galaxy to our own, and is classified as a dwarf elliptical galaxy, meaning that it has a smooth and almost featureless structure. Elliptical galaxies lack arms and notable pockets of star formation — both characteristic features of spiral galaxies. Dwarf ellipticals are quite common in groups and clusters of galaxies, and are often satellites of larger galaxies.

Because they lack stellar nurseries and contain mostly old stars, elliptical galaxies are often considered ‘dead’ when compared to their spiral relatives. However, astronomers have spotted signs of a population of young, blue stars at the centre of Messier 110 — hinting that it may not be so dead after all.

starsurfer wrote: ↑Thu Sep 19, 2019 9:55 am NGC 7098
https://www.astrobin.com/363768/B/
Copyright: Geoff Smith
ouCdKKIBGjla_1824x0_wmhqkGbg.jpg

Image Credit: ESO/Petr Horálek

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This week’s Picture of the Week showcases the bulging heart of the Milky Way as it hangs over the Chajnantor plateau. Located in the Atacama Desert of Chile, this plateau is one of the highest and driest places on Earth. This combination results in ideal conditions to observe millimetre and submillimetre radiation from space, which is usually strongly absorbed by Earth’s atmosphere. It is therefore no surprise that the Chajnantor plateau is home to the spectacularly productive Atacama Large Millimeter/submillimeter Array (ALMA), a state-of-the-art telescope that is studying light from some of the coldest objects in the Universe.

Above the intricate dust clouds and the frenzied glow of billions of stars, Mars, Saturn and the star Antares make a distinct triangle in the sky. The fuzzy green object to the left of the frame, nearly drowned out by the spectacular light of the Milky Way, is an interplanetary visitor called Comet 252P/LINEAR. This comet zoomed past Earth in April 2016 — although it was too faint for the unaided eye to see, its beauty is revealed in long-exposure images like this one.

However, as the intrepid stargazer standing front and centre in this image demonstrates, the plateau is also an excellent place for observing the cosmos with the naked eye. It provides views of the southern skies in breathtaking clarity, harking back to the days before artificial lights began to crowd the skies and drown out our view of the Universe.

Image Credit: ESA/Hubble & NASA, P. Cote et al.

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This image from the NASA/ESA Hubble Space Telescope shows the galaxy Messier 86. Despite its being discovered over 235 years ago by astronomer Charles Messier, the morphological classification of Messier 86 remains unclear; astronomers are still debating over whether it is either elliptical or lenticular (the latter being a cross between an elliptical and spiral galaxy).

Messier 86 is part of the Virgo Cluster of galaxies and is situated about 50 million light-years from Earth. The galaxy is moving through space remarkably quickly — its current trajectory is bringing it in our direction, back towards the centre of its cluster from the far side, at the incredible speed of over 875 000 kilometres per hour! Because of the speed with which it is moving through the cluster, Messier 86 is undergoing a process known as ram-pressure stripping; the resistive material filling the gaps between individual cluster galaxies is pulling at the gas and dust in Messier 86 and stripping them out as the galaxy moves, creating a long trail of hot gas that is emitting X-ray radiation.

Astronomers are using these data to study elliptical and lenticular galaxies, both of which are often found at the centres of galaxy clusters. By studying the cores of these galaxies, astronomers hope to determine details of the central structure and to analyse both the history of the galaxy and the formation of its core.

bystander wrote: ↑Mon Sep 23, 2019 7:11 pm Man Meets Milky Way
ESO Picture of the Week | 2019 Sep 23

Image Credit: ESO/Petr Horálek

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This week’s Picture of the Week showcases the bulging heart of the Milky Way as it hangs over the Chajnantor plateau. Located in the Atacama Desert of Chile, this plateau is one of the highest and driest places on Earth. This combination results in ideal conditions to observe millimetre and submillimetre radiation from space, which is usually strongly absorbed by Earth’s atmosphere. It is therefore no surprise that the Chajnantor plateau is home to the spectacularly productive Atacama Large Millimeter/submillimeter Array (ALMA), a state-of-the-art telescope that is studying light from some of the coldest objects in the Universe.

Above the intricate dust clouds and the frenzied glow of billions of stars, Mars, Saturn and the star Antares make a distinct triangle in the sky. The fuzzy green object to the left of the frame, nearly drowned out by the spectacular light of the Milky Way, is an interplanetary visitor called Comet 252P/LINEAR. This comet zoomed past Earth in April 2016 — although it was too faint for the unaided eye to see, its beauty is revealed in long-exposure images like this one.

However, as the intrepid stargazer standing front and centre in this image demonstrates, the plateau is also an excellent place for observing the cosmos with the naked eye. It provides views of the southern skies in breathtaking clarity, harking back to the days before artificial lights began to crowd the skies and drown out our view of the Universe.

Credit: ALMA (ESO/NAOJ/NRAO), P. Jachym (Czech Academy of Sciences) et al.

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Using the detailed eyes of the Atacama Large Millimeter / submillimeter Array (ALMA) and ESO’s Very Large Telescope (VLT), astronomers have mapped the intense tails of a cosmic jellyfish: a number of knotty streams of gas spewing outwards from a spiral galaxy named ESO 137-001.

This celestial cnidarian is shown here in beautiful detail. The various elements making up this image were captured by different telescopes. The galaxy and its surroundings were imaged by the NASA/ESA Hubble Space Telescope; its tails, which trace streams of hydrogen and show up in hues of bright purple, by the MUSE instrument mounted on the VLT; and bright hotspots of carbon dioxide emission from within the system, which show up as flares of orange-red, were spotted by ALMA.

These tails are caused by a dramatic phenomenon known as ram-pressure stripping. The space between galaxies in a cluster is not empty, but full of material that acts like a viscous fluid. As a galaxy travels through this resistant environment, gas is stripped out of the galaxy to form a wake that creates beautiful, intricate systems such as that seen here around ESO 137-001 (which resides in the Norma galaxy cluster). The direction and position of the tail shed light on the way in which the galaxy is moving — with galaxies usually falling towards the centre of the cluster itself. ...

• arXiv.org > astro-ph > arXiv:1905.13249 > 30 May 2019

Image Credit: ESA/Hubble & NASA, A. Adamo

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The galaxy pictured in this Hubble Picture of the Week has an especially evocative name: the Medusa merger.

Often referred to by its somewhat drier New General Catalogue designation of NGC 4194, this was not always one entity, but two. An early galaxy consumed a smaller gas-rich system, throwing out streams of stars and dust out into space. These streams, seen rising from the top of the merger galaxy, resembles the writhing snakes that Medusa, a monster in ancient Greek mythology, famously had on her head in place of hair, lending the object its intriguing name.

The legend of Medusa also held that anyone who saw her face would transform into stone. In this case, you can feast your eyes without fear on the centre of the merging galaxies, a region known as Medusa's eye. All the cool gas pooling here has triggered a burst of star formation, causing it to stand out brightly against the dark cosmic backdrop.

The Medusa merger is located about 130 million light-years away in the constellation of Ursa Major (The Great Bear).

Susanna Kohler wrote:

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What drives galaxies into different shapes and structures? To answer this question, we have to understand how the different components of galaxies form. In general, galaxies are made up of two main parts that form in different ways: a thin disk of stars, gas, and dust; and a thick spheroid of stars comprising a dense bulge and sparser halo. In a new study led by Min-Jung Park (Yonsei University, Republic of Korea), a team of scientists used a high-resolution cosmological simulation to explore these components of massive galaxies in more detail. In the image above, you’re seeing two views — face-on (top) and edge-on (bottom) — of a simulated massive, disk-dominated spiral galaxy. The left-most panels show the whole galaxy; the middle and right panels show the galaxy deconstructed into its spheroid (middle) and disk (right) components. By looking at these components separately, Park and collaborators are able to learn more about the processes that form these different parts of galaxies, shedding light on what causes galaxies’ final structures. To learn more about the authors’ conclusions, check out the article below.

• Astrophysical Journal 883(1):25 (2019 Sep 20) DOI: 10.3847/1538-4357/ab3afe
• arXiv.org > astro-ph > arXiv:1905.02216 > 06 May 2019 (v1), 13 Aug 2019 (v2)