Starship Asterisk*

NGC 7727’s Spectacular Galactic Dance ~ Image Credit: ESO / VLT

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ESO’s Very Large Telescope (VLT) has imaged the result of a spectacular cosmic collision — the galaxy NGC 7727. This giant was born from the merger of two galaxies, an event that started around a billion years ago. At its centre lies the closest pair of supermassive black holes ever found, two objects that are destined to coalesce into an even more massive black hole.

Just as you may bump into someone on a busy street, galaxies too can bump into each other. But while galactic interactions are much more violent than a bump on a busy street, individual stars don’t generally collide since, compared to their sizes, the distances between them are very large. Rather, the galaxies dance around each other, with gravity creating tidal forces that dramatically change the look of the two dance partners. ‘Tails’ of stars, gas and dust are spun around the galaxies as they eventually form a new, merged galaxy, resulting in the disordered and beautifully asymmetrical shape that we see in NGC 7727.

The consequences of this cosmic bump are spectacularly evident in this image of the galaxy, taken with the FOcal Reducer and low dispersion Spectrograph 2 (FORS2) instrument at ESO’s VLT. While the galaxy was previously captured by another ESO telescope, this new image shows more intricate details both within the main body of the galaxy and in the faint tails around it.

In this ESO VLT image we see the tangled trails created as the two galaxies merged, stripping stars and dust from each other to create the spectacular long arms embracing NGC 7727. Parts of these arms are dotted with stars, which appear as bright blue-purplish spots in this image.

Also visible in this image are two bright points at the centre of the galaxy, another telltale sign of its dramatic past. The core of NGC 7727 still consists of the original two galactic cores, each hosting a supermassive black hole. Located about 89 million light-years away from Earth, in the constellation of Aquarius, this is the closest pair of supermassive black holes to us. ...

Image Credit: Data: KPNO/NOIRLab/NSF/AURA
Processing: M. Zamani, A. Hussein, & D. de Martin (NSF NOIRLab)

The Triangulum Galaxy, otherwise known as Messier 33, lies almost 3 million light-years from Earth, and is a near neighbor of the Andromeda Galaxy. The galaxy is imaged here by the Nicholas U. Mayall 4-meter Telescope, located at Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab.

The Triangulum Galaxy is the third-largest member of the Local Group, a cluster of galaxies that includes our Milky Way and its closest neighbors. The Andromeda Galaxy is the largest member. The Triangulum Galaxy and Andromeda Galaxy have history together, but astronomers are still investigating the details. Their close proximity has caused some researchers to suggest that Triangulum is a satellite of the Andromeda Galaxy, not unlike the way the Moon is a satellite of the Earth — just on a much, much bigger scale. Alternatively, some researchers propose that these two galaxies may be independent and have simply brushed past each other, as evidenced by streams of stars and neutral hydrogen gas linking the two galaxies. However they have interacted, it’s probable that they will dramatically collide in 2.5 billion years, resulting in their consolidation and eventual evolution into a lenticular galaxy.

bystander wrote: ↑Wed Aug 17, 2022 11:28 pm Destined to Collide
NOIRLab Image of the Week | 2022 Aug 17

iotw2233a[1].jpgImage Credit: Data: KPNO/NOIRLab/NSF/AURA
Processing: M. Zamani, A. Hussein, & D. de Martin (NSF NOIRLab)

The Triangulum Galaxy, otherwise known as Messier 33, lies almost 3 million light-years from Earth, and is a near neighbor of the Andromeda Galaxy. The galaxy is imaged here by the Nicholas U. Mayall 4-meter Telescope, located at Kitt Peak National Observatory (KPNO), a Program of NSF’s NOIRLab.

The Triangulum Galaxy is the third-largest member of the Local Group, a cluster of galaxies that includes our Milky Way and its closest neighbors. The Andromeda Galaxy is the largest member. The Triangulum Galaxy and Andromeda Galaxy have history together, but astronomers are still investigating the details. Their close proximity has caused some researchers to suggest that Triangulum is a satellite of the Andromeda Galaxy, not unlike the way the Moon is a satellite of the Earth — just on a much, much bigger scale. Alternatively, some researchers propose that these two galaxies may be independent and have simply brushed past each other, as evidenced by streams of stars and neutral hydrogen gas linking the two galaxies. However they have interacted, it’s probable that they will dramatically collide in 2.5 billion years, resulting in their consolidation and eventual evolution into a lenticular galaxy.

ESA wrote:

Previous studies of the Local Group have combined observations from telescopes including the NASA/ESA Hubble Space Telescope and the ground-based Very Long Baseline Array to figure out how the orbits of Andromeda and Triangulum have changed over time. The two disc-shaped spiral galaxies are located between 2.5 and 3 million light-years from us, and are close enough to one another that they may be interacting.

Two possibilities emerged: either Triangulum is on an incredibly long six-billion-year orbit around Andromeda but has already fallen into it in the past, or it is currently on its very first infall. Each scenario reflects a different orbital path, and thus a different formation history and future for each galaxy....

By combining existing observations with the new data release from Gaia, the researchers determined how Andromeda and Triangulum are each moving across the sky, and calculated the orbital path for each galaxy both backwards and forwards in timefor billions of years.

“The velocities we found show that M33 cannot be on a long orbit around M31,” says co-author Ekta Patel of the University of Arizona, USA. “Our models unanimously imply that M33 must be on its first infall into M31.”

Image Credit: Zdenek Bardon/ESO/La Silla

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This picture of the week, taken from ESO’s La Silla Observatory in Chile, shows bright red streaks known as red sprites. These are an elusive form of lightning that occurs well-above storm clouds, discharging electricity high up in Earth’s atmosphere at an altitude of 50-90km. In addition to occurring much higher in the sky than regular lightning, they are cooler than the white lightning we usually see and appear much fainter. Red sprites are very difficult to catch: the first photographic evidence for them was only taken in 1989.

Seemingly painted across the background of the photograph is a green hue, known as airglow. During the day, sunlight knocks electrons away from nitrogen and oxygen in Earth’s atmosphere and, at night, these electrons recombine with the atoms and molecules, causing them to shine. Usually, airglow can only be seen in very dark skies where there is no light pollution.

This photograph was taken at the platform of ESO’s 3.6m telescope at La Silla in the middle of Chile’s Atacama desert. Because of its high altitude and lack of light pollution, La Silla is perfect for capturing these unusual phenomena.

Credit: ESA/Hubble & NASA, R. B. Tully, R. Jansen, R. Windhorst

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The galaxy featured in this Picture of the Week has a shape unlike many of the galaxies familiar to Hubble. Its thousands of bright stars evoke a spiral galaxy, but it lacks the characteristic ‘winding’ structure. The shining red blossoms stand out as well, twisted by clouds of dust — these are the locations of intense star formation. Yet it also radiates a diffuse glow, much like an elliptical galaxy and its core of older, redder stars. This galactic marvel is known to astronomers as NGC 1156.

NGC 1156 is located around 25 million light-years from Earth, in the constellation Aries. It has a variety of different features that are of interest to astronomers. A dwarf irregular galaxy, it’s also classified as isolated, meaning no other galaxies are nearby enough to influence its odd shape and continuing star formation. The extreme energy of freshly formed young stars gives colour to the galaxy, against the red glow of ionised hydrogen gas, while its centre is densely-packed with older generations of stars.

Hubble has captured NGC 1156 before — this new image features data from a galactic gap-filling programme simply titled “Every Known Nearby Galaxy”. Astronomers noticed that only three quarters of the galaxies within just over 30 million light-years of Earth had been observed by Hubble in sufficient detail to study the makeup of the stars within them. They proposed that in between larger projects, Hubble could take snapshots of the remaining quarter — including NGC 1156. Gap-filling programmes like this one ensure that the best use is made of Hubble’s valuable observing time.

Image Credit: ESO/Nogueras-Lara et al.

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This Picture of the Week shows an infrared view of Sagittarius B1, a region close to the centre of the Milky Way, imaged with ESO’s Very Large Telescope (VLT) in Chile. The centre of our galaxy is an exotic environment, densely populated with stars, and has been suggested to have more star formation than any other place in the Milky Way. But so far we have only found less than 10% of all young stars we expect there. Where are the others?

There is a catch: our view towards the centre is obscured by clouds of dust and gas, blocking the light from the stars. With infrared instruments it is possible to peer through these clouds. In this image, taken with the infrared HAWK-I instrument on ESO’s VLT, we get to take a closer look at this region. The view is mesmerising, unveiling a myriad of stars. In a recent study, a team led by Francisco Nogueras Lara (MPIA Heidelberg, Germany) discovered that this region hosts an excess of young stars, with a combined mass of more than 100 000 times the mass of the Sun. This is a key step forward in our quest to find all the expected young stars in the central regions of the Milky Way, and thus understand how stars evolve in such a unique environment.

This image comes from the GALACTICNUCLEUS survey, whose goal is to obtain high-resolution infrared images of the galactic centre. With future infrared ESO instruments such as ERIS on the VLT and MICADO on the upcoming ESO’s Extremely Large Telescope (ELT), the team hopes to study the stars in greater detail, which will lead to a better understanding of the evolution of the Milky Way’s centre.

• Nature Astronomy (25 Aug 2022) DOI: 10.1038/s41550-022-01755-3
• arXiv > astro-ph > arXiv:2207.02227 > 05 Jul 2022

Image Credit: ESA/Hubble & NASA, R. Chandar

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The arms of the spiral galaxy M74 are studded with rosy pink regions of fresh star formation in this image from the NASA/ESA Hubble Space Telescope. M74 — also known as the Phantom Galaxy — lies around 32 million light-years away from Earth in the constellation Pisces, and is a familiar sight for Hubble.

The beautiful reddish blooms that spread throughout M74 are huge clouds of hydrogen gas which are made to glow by the ultraviolet radiation from hot, young stars embedded within them. These regions — which astronomers refer to as H II regions — mark the location of recent star formation and are an important target for both space- and ground-based telescopes. Hubble’s Advanced Camera for Surveys (ACS), which collected the data in this image, even has a filter designed to pick out only this specific red wavelength of light!

The data in this image come from a set of observations exploring the evolution of local spiral galaxies such as M74, which aim to gain insights into the history of star formation in these spirals. To do this astronomers examined star clusters to date the different parts of spiral galaxies, enabling them to understand how the galaxies assembled over time. They also explored the distribution of dust in spiral galaxies; this dust is visible in this image as the dark threads winding along the spiral arms of M74.

Aside from their quest to understand the history of spiral galaxies, astronomers also observed M74 to complement observations from other telescopes. Combining observations of the same object from different telescopes across the electromagnetic spectrum gives astronomers far more insight than observations from a single telescope would. Hubble’s observations also paved the way for future instruments; M74 was one of the first targets of the powerful new NASA/ESA/CSA James Webb Space Telescope.

Multi-Observatory Views of M74

Image Credit: ESA/Webb, NASA & CSA, J. Lee and the PHANGS-JWST Team; ESA/Hubble & NASA, R. Chandar; Acknowledgement: J. Schmidt

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New images of the Phantom Galaxy, M74, showcase the power of space observatories working together in multiple wavelengths. On the left, the NASA/ESA Hubble Space Telescope’s view of the galaxy ranges from the older, redder stars towards the centre, to younger and bluer stars in its spiral arms, to the most active stellar formation in the red bubbles of H II regions. On the right, the NASA/ESA/CSA James Webb Space Telescope’s image is strikingly different, instead highlighting the masses of gas and dust within the galaxy’s arms, and the dense cluster of stars at its core. The combined image in the centre merges these two for a truly unique look at this “grand design” spiral galaxy.

Scientists combine data from telescopes operating across the electromagnetic spectrum to truly understand astronomical objects. In this way, data from Hubble and Webb compliment each other to provide a comprehensive view of the spectacular M74 galaxy.