Tag: galaxies

A spiral galaxy as seen from the side

9:36 am

A spiral galaxy seen from the side
Click for original image.

Cool image time! The picture to the right, reduced to post here, was taken by the Hubble Space Telescope of what is believed to be a spiral galaxy seen edge-on. The galaxy itself is estimated to be 150 million light years away, and this view highlights two major features, the dust lanes that run along the galaxy’s length and its distinct central nucleus, bulging out from the galaxy’s flat plain.

The way this image was produced however is intriguing on its own:

Like most of the full-colour Hubble images released by ESA/Hubble, this image is a composite, made up of several individual snapshots taken by Hubble at different times and capturing different wavelengths of light. … A notable aspect of this image is that the two sets of Hubble data used were collected 23 years apart, in 2000 and 2023! Hubble’s longevity doesn’t just afford us the ability to produce new and better images of old targets; it also provides a long-term archive of data which only becomes more and more useful to astronomers.

All told, four Hubble data sets were used to produce the picture.

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Post-collision images of two galaxies

10:56 am

Post-collision imagery by Hubble and Webb
Click for original image.

Using both the Hubble and Webb space telescopes, astronomers have now produced multi-wavelength images of the galaxies NGC 2207and IC 2163, as shown to the right.

Millions of years ago the smaller galaxy, IC 2163, grazed against the larger, NGC 2207, resulting today in increased star formation in both galaxies, indicated by blue in the Hubble photo. From the caption of the combined images:

Combined, they are estimated to form the equivalent of two dozen new stars that are the size of the Sun annually. Our Milky Way galaxy forms the equivalent of two or three new Sun-like stars per year. Both galaxies have hosted seven known supernovae, each of which may have cleared space in their arms, rearranging gas and dust that later cooled, and allowed many new stars to form.

The two images to the left leaves the Hubble and Webb separate, making it easier to see the different features the different wavelengths reveal. From this caption:

In Hubble’s image, the star-filled spiral arms glow brightly in blue, and the galaxies’ cores in orange. Both galaxies are covered in dark brown dust lanes, which obscure the view of IC 2163’s core at left. In Webb’s image, cold dust takes centre stage, casting the galaxies’ arms in white. Areas where stars are still deeply embedded in the dust appear pink. Other pink dots may be objects that lie well behind these galaxies, including active supermassive black holes known as quasars.

The largest and brightest pink area in the Webb image, on the bottom right and a blue patch in the Hubble image, is where a strong cluster of star formation is presently occurring.

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Astronomers find another galaxy that shouldn’t be there in the early universe

9:44 am

REBELS-25
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The uncertainty of science: Using ground-based telescopes, astronomers have identified a galaxy only 700 million years after the Big Bang that is far more organized and coherent in shape and structure than thought possibly that soon after the theorized creation of the universe.

The galaxy in question is dubbed REBELS-25. It is at a red shift of z=7.31, which means that it is from a time when the universe was only 700 million years old. The earliest galaxies ever seen are only a few hundred million years older.

REBELS by name rebel by nature. This odd galaxy has stumped astronomers because it shows evidence of an ordered structure and rotation. It may even have a central elongated bar and spiral arms, though further observation is needed to confirm these structures.

This is in contrast to the small, messy, lumpy and chaotic norm for galaxies of a similar age. “According to our understanding of galaxy formation, we expect most early galaxies to be small and messy looking,” says co-author Jacqueline Hodge, an astronomer at Leiden University in the Netherlands.

You can read the published paper here [pdf]. The picture to the right shows this galaxy as seen by the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile.

The consensus view of the early universe said there would not have been enough time for such a structured galaxy to form. And yet as astronomers use the improved astronomical instrumentation of our time to look deeper and deeper at that early universe, they keep finding things — like this galaxy — that defy that consensus view.

The answer to this mystery remains unknown, and is likely not yet answerable with the data we presently have. The data we do have however is beginning to suggest that scientists might have to begin looking at fundamentally different theories as to the inital formation of the universe. The Big Bang might still work, but if so it might require a major rewrite.

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The jet 3,000 light years long that causes nearby stars to explode

10:48 am

The jet from M87
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Cool image time! The picture to the left, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope of the giant eliptical galaxy M87, known for more than a century by astronomers for the jet of gas that points outward from its center. Astronomers now know that this jet is produced by a supermassive black hole in the center of M87, weighing 6.5 billion times the mass of our Sun.

The blowtorch-like jet seems to cause stars to erupt along its trajectory. These novae are not caught inside the jet, but are apparently in a dangerous neighbourhood nearby. During a recent 9-month survey, astronomers using Hubble found twice as many of these novae going off near the jet as elsewhere in the galaxy. The galaxy is the home of several trillion stars and thousands of star-like globular star clusters.

M87 is considered an old galaxy, but its entire formation process remains uncertain.

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Webb takes an infrared look at a galaxy looked at by Hubble

12:21 pm

Comparing Hubble with Webb
For original images go here and here.

Cool image time! The bottom picture on the right, cropped to post here, is a just released false color infrared image of the galaxy Arp 107, taken by the Webb Space Telescope. The picture at the top is a previously released optical image taken by the Hubble Space Telescope and featured as a cool image back in September 2023. The Hubble image was taken as part of a survey project to photograph the entire Arp catalog of 338 “peculiar galaxies,” put together by astronomer Halton Arp in 1966. In this case Arp 107 is peculiar because it is actually two galaxies in the process of merging. It is also peculiar because the galaxy on the left has an active galactic nuclei (AGN), where a supermassive black hole is sucking up material and thus emitting a lot of energy.

The Webb infrared image was taken to supplement that optical image. The blue spiral arms indicate dust and star-forming regions. The bright orange object in the center of the galaxy is that AGN, clearly defined by Webb’s infrared camera.

When I posted the Hubble image in 2023, I noted that “if you ignore the blue whorls of the left galaxy, the two bright cores of these merging galaxies are about the same size.” In the Webb image the two cores still appear about the same size, but in the infrared they produce emissions in decidedly different wavelengths, as shown by the different false colors of orange and blue. The core of the galaxy on the right is dust filled and forming stars, while the core of the left galaxy appears to have less dust with all of its emissions resulting from the energy produced by the material being pulled into the supermassive black hole.

The universe is very active and changing, but to understand that process we humans have to look at everything across the entire electromagnetic spectrum, not just in the optical wavelengths our eyes see.

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What the Milky Way would look like if it was presently a star forming powerhouse

9:15 am

A galaxy as seen by Hubble and Webb
For the original images go here and here.

Cool image time! The two pictures to the right, taken respectively by the Hubble and Webb space telescopes of the same galaxy, shows us many different features of a barred galaxy, located about 35 million light years away. From the caption for the Hubble image:

This picture is composed of a whopping ten different images taken by the Hubble Space Telescope, each filtered to collect light from a specific wavelength or range of wavelengths. It spans Hubble’s sensitivity to light, from ultraviolet around 275 nanometres through blue, green and red to near-infrared at 1600 nanometres. This allows information about many different astrophysical processes in the galaxy to be recorded: a notable example is the red 656-nanometre filter used here. Hydrogen atoms which get ionised can emit light at this particular wavelength, called H-alpha emission. New stars forming in a molecular cloud, made mostly of hydrogen gas, emit copious amounts of ultraviolet light which is absorbed by the cloud, but which ionises it and causes it to glow with this H-alpha light.

Therefore, filtering to detect only this light provides a reliable means to detect areas of star formation (called H II regions), shown in this image by the bright red and pink colours of the blossoming patches filling NGC 1559’s spiral arms.

The Z-shaped blue indicates the stars and its most distinct spiral arms. Astronomers presently believe that the Milky Way is also a barred spiral like this, though its star-forming regions are thought to be far less extensive and distinct.

The Webb infrared image matches the Hubble data, with the false color blue indicating the near-infrared and the false color red the mid-infrared. As with the Hubble picture, the red indicates the galaxy’s extensive star forming regions.

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A galaxy with a halo and a stupendous central black hole

9:22 am

A galaxy with a halo and a stupendous black hole
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope as part of a survey of galaxies that have what astronomers call active galactic nuclei (AGNs). This galaxy, dubbed IC 4709, is about 240 million light years away.

If IC 4709’s core were just filled with stars, it would not be nearly so bright. Instead it hosts a gargantuan black hole, 65 million times the mass of our Sun. A disc of gas spirals around and eventually into this black hole, with the gas crashing together and heating up as it spins. It reaches such high temperatures that it emits vast quantities of electromagnetic radiation, from infrared to visible to ultraviolet light and beyond — in this case including X-rays. The AGN in IC 4709 is obscured by a lane of dark dust, just visible at the centre of the galaxy in this image, which blocks any optical emission from the nucleus itself.

To get a very vague sense of scale, this supermassive black hole is more than sixteen times more massive than the relatively inactive supermassive black hole in the center of the Milky Way. This imagery and data from Hubble will help astronomers better understand the interaction between the black hole and its surrounding galaxy.

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A real whirlpool in space

9:52 am

A real whirlpool in space
Click for original image.
Cool image time! The picture above, cropped to post here, was taken by the Hubble Space Telescope as part of a survey of nearby galaxies that have what astronomers call an Active Galactic Nuclei (AGN), because the supermassive black hole at the center is devouring nearby material at a great rate and thus producing high energy emissions as it does so.

Many active galaxies are known to astronomers at vast distances from Earth, thanks to the great brightness of their nuclei highlighting them next to other, dimmer galaxies. At 128 million light-years from Earth, UGC 3478 is positively neighbourly to us. The data used to make this image comes from a Hubble survey of nearby powerful AGNs found in relatively high-energy X-rays, like this one, which it is hoped can help astronomers to understand how the galaxies interact with the supermassive black holes at their hearts.

The bottom line is that this spiral galaxy literally is a whirlpool, the entire galaxy spiralling down into that massive black hole in its center. One cannot help wondering why such galaxies don’t end up eventually getting completely swallowed by that black hole.

Or maybe they do, and we don’t see such things because all that is left is a supermassive black hole that emits no light or energy at all, a dark silent ghost traveling between the galaxies unseen and undetectable.

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A galaxy with a ring

9:34 am

A galaxy with a ring
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Cool image time! The photo to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope, and appears part of a long term survey of nearby ringed galaxies. From the caption:

MCG+07-07-072 has quite an unusual shape, for a spiral galaxy, with thin arms emerging from the ends of its barred core to draw a near-circle around its disc. It is classified, using a common extension of the basic Hubble scheme, as an SBc(r) galaxy: the c denotes that its two spiral arms are loosely wound, each only performing a half-turn around the galaxy, and the (r) is for the ring-like structure they create. Rings in galaxies come in quite a few forms, from merely uncommon, to rare and astrophysically important!

Lenticular galaxies are a type that sit between elliptical and spiral galaxies. They feature a large disc, unlike an elliptical galaxy, but lack any spiral arms. Lenticular means lens-shaped, and these galaxies often feature ring-like shapes in their discs. Meanwhile, the classification of “ring galaxy” is reserved for peculiar galaxies with a round ring of gas and star formation, much like spiral arms look, but completely disconnected from the galactic nucleus – or even without any visible nucleus! They’re thought to be formed in galactic collisions.

This galaxy is about 320 million light years away, and is also known as Abell 426. Though astronomers think that these various shapes of galaxies, from barred to lenticular to ringed, are formed from a variety of galactic collusions and interactions with each galaxy’s nucleus, that remains nothing more than an educated guess. The complexity of galaxy evolution, involving billions of years and millions of stars, is barely in its infancy, and requires a lot of assumptions because our observations only involves a mere nanosecond in that grand history.

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A supernova overpowers a spiral galaxy

9:34 am

A supernova overwhelms a small galaxy

Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken in early 2023 by the Hubble Space Telescope because a ground-based automated sky survey had detected a new supernovae in late 2022 in this galaxy. The spiral galaxy is dubbed LEDA 857074, and is interesting because of its bright central bar and dim and broken spiral arms.

That supernova is the bright spot inside the galaxy’s central bar. It is so bright that it almost looks like someone accidently pasted a white dot there using a graphics program. From the caption:

Astronomers have catalogued millions of galaxies, so while today tens of thousands of supernovae are detected annually, the chance that one is spotted in any particular galaxy is slim. We also do not know how actively LEDA 857074 is forming stars, and therefore how often it might host a supernova. This galaxy is therefore an unlikely and lucky target of Hubble, thanks to this supernova shining a spotlight on it! It now joins the ranks of many more famous celestial objects, with its own Hubble image.

The galaxy itself had been studied by almost no one until this supernova was discovered in it.

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A classic spiral galaxy

8:53 am

A classic spiral galaxy
Click for original image.

Monday is always a slow news day in space, so we start the day with a cool image. The picture to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope of a spiral galaxy about 100 million light years from Earth.

That NGC 3430 is such a fine example of a galactic spiral may be why it ended up as part of the sample that Edwin Hubble used to define his classification of galaxies. Namesake of the Hubble Space Telescope, in 1926 he authored a paper which classified some four hundred galaxies by their appearance — as either spiral, barred spiral, lenticular, elliptical or irregular. This straightforward typology proved immensely influential, and the modern, more detailed schemes that astronomers use today are still based on it. NGC 3430 itself is an SAc galaxy, a spiral lacking a central bar with open, clearly-defined arms.

The bright blue indicates areas of star formation, while the reddish streaks indicates dust. The orange/reddish dots above and below the galaxy are distant background galaxies whose light has been shifted to the red because they appear to be moving away from us due to the expansion rate of the universe.

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Astronomers see a quiet galaxy become active for the first time

9:46 am

Using a number of space- and ground-based telescopes, astronomers have for the first time seen in real time what had previously been a very inactive and quiet galaxy become active and energetic, suggesting a major event at the galaxy’s center had taken place to change its behavior.

From the abstract of the paper [pdf]:

We conclude that the variations observed in SDSS1335+0728 could be either explained by a ∼ 10 6 M ⊙ AGN [a one million solar mass black hole] that is just turning on or by an exotic tidal disruption event (TDE). If the former is true, SDSS1335+0728 is one of the strongest cases of an AGN observed in the process of activating. If the latter were found to be the case, it would correspond to the longest and faintest TDE ever observed (or another class of still unknown nuclear transient). Future observations of SDSS1335+0728 are crucial to further understand its behaviour.

As noted in the press release:

Some phenomena, like supernova explosions or tidal disruption events — when a star gets too close to a black hole and is torn apart — can make galaxies suddenly light up. But these brightness variations typically last only a few dozen or, at most, a few hundreds of days. SDSS1335+0728 is still growing brighter today, more than four years after it was first seen to ‘switch on’. Moreover, the variations detected in the galaxy, which is located 300 million light-years away in the constellation Virgo, are unlike any seen before.

If the central black hole is switching from being quiet to active, this galaxy is providing astronomers critical information for understanding such changes. This is particularly important to us here in the Milky Way, which has a very inactive central supermassive black hole weighing about 4 million solar masses. It would be very useful to understand what would cause it to become active, especially because such an event might even have an impact — possibly negative — throughout our entire galaxy.

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Astronomers find another record-setting most distant galaxy

9:42 am

The uncertainty of science: Using the Webb Space Telescope, astonomers have identified another record-setting most distant galaxy, believed to exist only 300 million years after the Big Bang and once again far more massive and developed than expected that early in the universe.

The galaxy was actually one of two very early galaxies identified that lie close to each other on the sky but are not linked in any way.

The two record-breaking galaxies are called JADES-GS-z14-0 and JADES-GS-z14-1, the former being the more distant of the two. In addition to being the new distance record holder, JADES-GS-z14-0 is remarkable for how big and bright it is. “The size of the galaxy clearly proves that most of the light is being produced by large numbers of young stars,” said Eisenstein, a Harvard professor and chair of the astronomy department, “rather than material falling onto a supermassive black hole in the galaxy’s center, which would appear much smaller.”

The combination of the extreme brightness and the fact that young stars are fueling this high luminosity makes JADES-GS-z14-0 the most striking evidence yet found for the rapid formation of large, massive galaxies in the early Universe.

All the early galaxies that Webb has found so far have been far more massive and developed than cosmologists had predicted. The expectation had been that there wouldn’t have been enough time after the Big Bang for such galaxies to develop. Yet they have, suggesting something is not right with our theories about the beginning of the universe.

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Visiting a galactic bar

9:27 am

Visiting a galactic bar
Click for original image.

Cool image time! The picture to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope as part of a research project studying the flow of gases inside barred galaxies. It shows a spiral galaxy, NGC 4731, edge on, located about 43 million light years away. From the caption:

Barred spiral galaxies outnumber both regular spirals and elliptical galaxies put together, numbering around 60% of all galaxies. The visible bar structure is a result of orbits of stars and gas in the galaxy lining up, forming a dense region that individual stars move in and out of over time. This is the same process that maintains a galaxy’s spiral arms, but it is somewhat more mysterious for bars: spiral galaxies seem to form bars in their centres as they mature, accounting for the large number of bars we see today, but can also lose them later on as the accumulated mass along the bar grows unstable. The orbital patterns and the gravitational interactions within a galaxy that sustain the bar also transport matter and energy into it, fuelling star formation.

Astronomers don’t really understand why these barred structures develop, since you would expect the overall gravity of the galaxy would promote a spiral or spherical shape. There must are factors not yet understood or completely identified (such as the magnetic fields of such galaxies).

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A galaxy’s net of dust

10:02 am

A galaxy's net of dust
Click for full image.

Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope of the central part of galaxy NGC 4753, 60 million light years away and known as a lenticular galaxy because of its elongated elliptical shape and ill-defined spiral arms. It is believed we looking at this galaxy edge-on.

You can see a wider image of NGC 4753 here, released in January and taken by the Gemini South telescope in Chile. According to that press release, the brown dust lanes that seem to form a wavy net in the foreground are created by a process called differential precession:

Precession occurs when a rotating object’s axis of rotation changes orientation, like a spinning top that wobbles as it loses momentum. And differential means that the rate of precession varies depending on the radius. In the case of a dusty accretion disk orbiting a galactic nucleus, the rate of precession is faster toward the center and slower near the edges. This varying, wobble-like motion results from the angle at which NGC 4753 and its former dwarf companion collided and is the cause of the strongly twisted dust lanes we see wrapped around the galaxy’s luminous nucleus today.

Once again, the limitation of only observing this object from one angle makes it very difficult to untangle what it really looks like. Therefore, these conclusions carry a great deal of uncertainty.

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The spiral dust streams within the Andromeda galaxy

10:15 am

Andromeda in infrared
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Cool image time! The picture above, cropped and reduced to post here, was released yesterday and uses archival infrared data from the now retired Spitzer Space telescope to highlight the dust found within the Andromeda galaxy, about two million light years away.

Spitzer’s infrared view was similar to Webb’s but at a far lower resolution. In the picture above the red indicates cool dust.

By separating these wavelengths and looking at the dust alone, astronomers can see the galaxy’s “skeleton” — places where gas has coalesced and cooled, sometimes forming dust, creating conditions for stars to form. This view of Andromeda revealed a few surprises. For instance, although it is a spiral galaxy like the Milky Way, Andromeda is dominated by a large dust ring rather than distinct arms circling its center. The images also revealed a secondary hole in one portion of the ring where a dwarf galaxy passed through.

The data also suggested that the dust is flowing at a very steady rate into Andromeda’s central black hole. According to computer simulations, this steady rate would explain why the supermassive black holes at the center of both Andromeda and the Milky Way are relative inactive. If the dust fell in clumps rather than a steady flow, both black holes would exhibit bursts of high activity, similar to active galactic centers.

A side note for anyone wishing to star-gaze: Andromeda is actually the largest visible galaxy in the night sky, about six times with width of the full Moon. If you can get to a very dark-sky location, get your eyes very dark-adapted, and you know where to look, you can actually see it with the naked eye. I did this once at a star party, helped by a bunch of amateur astronomers. The galaxy is very faint, and it helps to use binoculars to help locate it, but once identified its size in the sky truly is breath-taking.

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A supernova factory

9:44 am

A supernova factory

Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope in 2023 as part of a survey of galaxies where recent supernovae have occurred. One occurred in 2020 in this galaxy, which is about 240 million light years away and dubbed UGC 9684.

Remarkably, the 2020 supernova in this galaxy isn’t the only one that’s been seen there — four supernova-like events have been spotted in UGC 9684 since 2006, putting it up there with the most active supernova-producing galaxies. It turns out that UGC 9684 is a quite active star-forming galaxy, calculated as producing one solar mass worth of stars every few years! This level of stellar formation makes UGC 9684 a veritable supernova factory, and a galaxy to watch for astronomers hoping to examine these exceptional events.

This image provides scientists a high resolution baseline should another supernova occur. It will not only make it easier to spot a future supernova, it also increases the chances that the progenitor star that went boom could be identified.

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Patchy arms in a nearby spiral galaxy

9:16 am

Patchy arms in spiral galaxy
Click for original image.

Cool image time! The photo to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope to study this southern hemisphere galaxy in detail. The galaxy, dubbed ESO 422-41, is located about 34 million light years away, and thus is a relatively close neighbor. From the caption:

A spiral galaxy, with a brightly shining core and two large arms. The arms are broad, faint overall and quite patchy, and feature several small bright spots where stars are forming. A few foreground stars with small diffraction spikes can be seen in front of the galaxy.

The patchy nature of the two arms makes each somewhat indistinct, so that at first glance this galaxy looks more like a elliptical blob, until you look close and notice those arms winding around that bright core. And as patchy as those arms are, the patches of blue are regions where new stars are forming.

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A whirlpool half-hidden by dust

10:23 am

A whirlpool half-hidden by dust
Click for original image.

Cool image time! The picture to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope and shows us a magnificent spiral galaxy about 100 million light years away that also has very active nucleus at its center as well as many star-forming regions (in blue) in its outer arms.

That we do not see the same blue spiral arms on the right side of the photo is not because they are lacking, but because a very large stream of dust blocks our view.

This dark nebula is part of the Chamaeleon star-forming region, itself located only around 500 light-years from us, in a nearby part of the Milky Way galaxy. The dark clouds in the Chamaeleon region occupy a large area of the southern sky, covering their namesake constellation but also encroaching on nearby constellations, like Apus. The cloud is well-studied for its treasury of young stars, particularly the cloud Cha I, which has been imaged by Hubble and also by the … James Webb Space Telescope.

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Interacting galaxies

9:27 am

Interacting galaxies
Click for original image.

Cool image time! The picture to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope as part of a dark energy survey. It shows two galaxies very close together, their perpheries only about 40,000 light years apart, with the larger galaxy about the size of the Milky Way.

For comparison, the Large Magellanic Cloud (LMC) is about 167,000 light years from the Milky Way, more than four times farther that this satellite galaxy. Yet the satellite galaxy here appears much larger than the LMC, having a central core that the LMC lacks. From the caption:

Given this, coupled with the fact that NGC 5996 is roughly comparable in size to the Milky Way, it is not surprising that NGC 5996 and NGC 5994 — apparently separated by only 40 thousand light-years or so — are interacting with one another. In fact, the interaction might be what has caused the spiral shape of NGC 5996 to distort and apparently be drawn in the direction of NGC 5994. It also prompted the formation of the very long and faint tail of stars and gas curving away from NGC 5996, up to the top right of the image. This ‘tidal tail’ is a common phenomenon that appears when galaxies get in close together, as can be seen in several Hubble images.

In this single picture we are witnessing evidence of a process that has been going on for likely many millions of years.

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Is this really a spiral galaxy?

10:16 am

Is this really a spiral galaxy?

The uncertainty of science: The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope and released on March 4, 2024 by the PR department of the European Space Agency (ESA) as part of its Hubble Picture of the Week program. It shows what the press release claims is a spiral galaxy about 55 million light years away, seen edge on.

In this image NGC 4423 appears to have quite an irregular, tubular form, so it might be surprising to find out that it is in fact a spiral galaxy. Knowing this, we can make out the denser central bulge of the galaxy, and the less crowded surrounding disc (the part that comprises the spiral arms).

If NGC 4423 were viewed face-on it would resemble the shape that we most associate with spiral galaxies: the spectacular curving arms sweeping out from a bright centre, interspersed with dimmer, darker, less populated regions. But when observing the skies we are constrained by the relative alignments between Earth and the objects that we are observing: we cannot simply reposition Earth so that we can get a better face-on view of NGC 4423!

This picture provides a great example of the amount of assumptions that are often contained in astronomical observations. Though the data strongly suggests this is spiral, we must remember this is merely an educated guess, based on that central bulge and the dust lanes visible along the galaxy’s profile. There is actually no guarantee that this is so. As the press release also notes, astronomers are constrained by our viewpoint, and cannot change that viewpoint to get a better view to confirm this guess. For all we know, a face on veiw of this flat galaxy would reveal it has no spiral arms, but instead is mottled and chaotic, a rare type that does exist.

Astronomers do the best they can, but it is important that they (and we) always recognize the limitations.

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A galaxy with a tail of star-forming clusters

10:34 am

A galaxy with a tail of newborn stars
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Cool image time! The picture to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope as part of a survey of twelve different galaxies that have long tails. In this case, the galaxy is named Arp-Madore 1054-325, and the tail that trails off in the upper left is caused by the gravity of the nearby neighboring galaxy, which I think is the patch of stars just below it. Within it are many star clusters where new stars are forming. From the caption:

A team of astronomers used a combination of new observations and archival data to get ages and masses of tidal tail star clusters. They found that these clusters are very young — only 10 million years old. And they seem to be forming at the same rate along tails stretching for thousands of light-years. “It’s a surprise to see lots of the young objects in the tails. It tells us a lot about cluster formation efficiency,” said lead author Michael Rodruck of Randolph-Macon College in Ashland, Virginia.

Before the mergers, the galaxies were rich in dusty clouds of molecular hydrogen that may have simply remained inert. But the clouds got jostled and bumped into each other during the encounters. This compressed the hydrogen to the point where it precipitated a firestorm of star birth.

In some ways this galaxy portends one possible future of the Milky Way, after it collides with the nearby Andromeda galaxy in the far future.

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A soft but dim spiral

10:51 am

A soft but dim spiral
Click for original image.

Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope as part of a survey of nearby galaxies in which supernovae had previously been detected.

This softly luminous galaxy — lying in the constellation Hercules, about 110 million light-years from Earth — seems outshone by the sparkling foreground stars that surround it. The type II supernova which took place in this galaxy in 2019, while no longer visible in this image, definitely outshone the galaxy at the time!

What amazes me about this somewhat dim spiral galaxy is its beautiful structure, its two spiral arms coiling outward in perfect symmetry. And yet, we are looking at a object that is almost entirely empty space, hundreds of thousands of light years across. Somehow the almost infinitesimal force of gravity at those distances is still able to shape the arms, and the spirals.

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The internal structure of 19 galaxies, as seen in the infrared by Webb

9:48 am

The internal structure of 19 galaxies, as seen by Webb
Click for original image.

Scientists using the Webb Space Telescope today released false color infrared images of nineteen different spiral galaxies, each showing the complex internal structure that traces of spiral arms, but not always.

A compliation of those infrared images is to the right, reduced and sharpened to post here.

[Webb]’s NIRCam (Near-Infrared Camera) captured millions of stars in these images, which sparkle in blue tones. Some stars are spread throughout the spiral arms, but others are clumped tightly together in star clusters.

The telescope’s MIRI (Mid-Infrared Instrument) data highlights glowing dust, showing us where it exists behind, around, and between stars. It also spotlights stars that have not yet fully formed – they are still encased in the gas and dust that feed their growth, like bright red seeds at the tips of dusty peaks. “These are where we can find the newest, most massive stars in the galaxies,” said Erik Rosolowsky, a professor of physics at the University of Alberta in Edmonton, Canada.

The data suggests, not unexpectedly, that the central parts of each galaxy are older, formed first, with starbirth occurring later in the outer regions. A lot of further analysis however will be required to understand all the patterns exhibited in these images and their larger significance in connection with galaxy formation.

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Merging galaxies

10:02 am

Merging galaxies
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Time for another cool image from the Hubble Space Telescope. The picture to the right, cropped, reduced, and sharpened to post here, was taken by Hubble to study “the overall physical characteristics of galaxies and their star formation.”

What the picture however reveals best is the ongoing merger of three galaxies.

Arp 300 consists of two interacting galaxies, UGC 05028 (the smaller face-on spiral galaxy) and UGC 05029 (the larger face-on spiral). Likely due to its gravitational dance with its larger partner, UGC 05028 has an asymmetric, irregular structure, which is not as visible from ground-based telescopes but is quite distinct in this new image from NASA’s Hubble Space Telescope. The bright knot visible to the southeast of the center of UGC 05028 may be the remnant of another small galaxy that is in the process of merging with that galaxy.

As always with Hubble galaxy images, there are a plethora of other background galaxies scattered about, including what appears to be another merger in the center right of two elliptical galaxies. In fact, except for one star in the lower right (with the four spikes), every other object in this photo is a galaxy of many shapes and distances.

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Webb confirms the unusual shape of early galaxies as seen by Hubble

9:52 am

Earth galaxies shapes, as seen by Webb in infrared
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The uncertainty of science: The infrared view of the Webb Space Telescope appears to have confirmed and even underlined the unusual shapes of many early galaxies as previously seen by the Hubble Space Telescope.

Researchers analyzing images from NASA’s James Webb Space Telescope have found that galaxies in the early universe are often flat and elongated, like surfboards and pool noodles – and are rarely round, like volleyballs or frisbees. “Roughly 50 to 80% of the galaxies we studied appear to be flattened in two dimensions,” explained lead author Viraj Pandya, a NASA Hubble Fellow at Columbia University in New York. “Galaxies that look like pool noodles or surfboards seem to be very common in the early universe, which is surprising, since they are uncommon nearby.”

The team focused on a vast field of near-infrared images delivered by Webb, known as the Cosmic Evolution Early Release Science (CEERS) Survey, plucking out galaxies that are estimated to exist when the universe was 600 million to 6 billion years old.

While most distant galaxies look like surfboards and pool noodles, others are shaped like frisbees and volleyballs. The “volleyballs,” or sphere-shaped galaxies, appear the most compact type on the cosmic “ocean” and were also the least frequently identified. The frisbees were found to be as large as the surfboard- and pool noodle-shaped galaxies along the “horizon,” but become more common closer to “shore” in the nearby universe.

The galaxies also appear generally far less massive than galaxies in the near universe, which fits with the Big Bang theory that says they had less time to grow.

The press release notes that the sample size is still very small, and further observations will be required to confirm whether these shapes are common in the early universe.

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One spiral galaxy eating another

9:51 am

One spiral galaxy eating another
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Cool image time! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope as part of an on-going survey of known pecular-looking galaxies. This pair is believed to be 570 million light years away. From the caption:

Galaxies are composed of stars and their solar systems, dust and gas. In galactic collisions, therefore, these constituent components may experience enormous changes in the gravitational forces acting on them. In time, this completely changes the structure of the two (or more) colliding galaxies, and sometimes ultimately results in a single, merged galaxy. That may well be what results from the collision pictured in this image. Galaxies that result from mergers are thought to have a regular or elliptical structure, as the merging process disrupts more complex structures (such as those observed in spiral galaxies). It would be fascinating to know what Arp 122 will look like once this collision is complete . . . but that will not happen for a long, long time.

From our viewpoint, the spiral galaxy at the top appears warped by the gravitational pull of the face-on spiral at the bottom, as if it is being sucked into the bottom galaxy. In truth, both galaxies are pulling on each other. If we could circle around and see them in three dimensions we would almost certainly see distortions in the bottom spiral as well.

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Galaxies galore, near and far

9:08 am

Galaxies galore, and near and far

Cool image for the day after Christmas! The picture to the right, reduced and sharpened to post here, was taken by the Hubble Space Telescope, and shows a cluster of galaxies that all seem near each other. However, as the caption notes,

[W]hilst NGC 1356 [the largest spiral] and LEDA 95415 [close by its left] appear to be so close that they must surely be interacting, the former is about 550 million light-years from Earth and the latter is roughly 840 million light-years away, so there is nearly a whopping 300 million light-year separation between them. That also means that LEDA 95415 is likely nowhere near as [small] as it appears to be.

On the other hand, whilst NGC 1356 and IC 1947 [farthest to the left] seem to be separated by a relative gulf in this image, IC 1947 is only about 500 million light-years from Earth. The angular distance apparent between them in this image only works out to less than four hundred thousand light-years, so they are actually much much closer neighbours in three-dimensional space than NGC 1356 and LEDA 95415!

The two galaxies farthest apart in this image are actually close enough together to interact significantly. Though this picture doesn’t have the resolution to see it, there is likely a stream of stars between the two.

Note also the numerous tiny other galaxies scatterered throughout the picture. In fact, except for three stars (the objects with the north-south-east-west spikes), every object is a galaxy holding stars too numerous to count.

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A galaxy of violence

9:53 am

A galaxy of violence
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Time for another cool image! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope, and shows a well defined spiral galaxy face-on in optical wavelengths.

This whirling image features a bright spiral galaxy known as MCG-01-24-014, which is located about 275 million light-years from Earth. In addition to being a well-defined spiral galaxy, MCG-01-24-014 has an extremely energetic core, known as an active galactic nucleus (AGN), so it is referred to as an active galaxy. Even more specifically, it is categorised as a Type-2 Seyfert galaxy. Seyfert galaxies host one of the most common subclasses of AGN, alongside quasars. Whilst the precise categorisation of AGNs is nuanced, Seyfert galaxies tend to be relatively nearby ones where the host galaxy remains plainly detectable alongside its central AGN, while quasars are invariably very distant AGNs whose incredible luminosities outshine their host galaxies.

In contrast, the core of our own Milky Way galaxy is very quiet, which is likely a factor in why it was possible for life to form on Earth.

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Galaxies in a row

9:18 am

Galaxies in a row
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Cool image time from Hubble! The picture to the right, cropped, reduced, and sharpened to post here, was taken by the Hubble Space Telescope as part of a survey of nearby “pecular” galaxies. What makes it unusual is the line of distant galaxies below the largest on the left.

The wonderful quality of this image also reveals several further galaxies, not associated with this system but fortuitously positioned in such a way that they appear to be forming a line that approaches the leftmost (in this image) component of Arp-Madore 2105-332, which is known individually as 2MASX J21080752-3314337. The rightmost galaxy, meanwhile, is known as 2MASX J21080362-3313196. These hefty names do not lend themselves to easy memorisation, but they do actually contain valuable information: they are coordinates in the right ascension and declination system used widely by astronomers to locate astronomical objects.

Both larger galaxies are thought to be about 200 million light years away, with the smaller ones far more distant. If you look at the full resolution image, you will see that there are at least six galaxies in that line, one that appears to be an elliptical galaxy with all the rest a variety of different types of spiral galaxies. The detail provided by Hubble is truly astonishing.

Though they are not linked to the larger galaxies, it is not clear if they are linked to each other.

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