spiral galaxies – Behind The Black

A classic spiral galaxy

July 22, 2024 8:53 am Robert Zimmerman

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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.

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

January 29, 2024 9:48 am Robert Zimmerman

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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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Spirals within spirals

July 24, 2023 8:58 am Robert Zimmerman

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Cool image time! The picture to the right, cropped, reduced, and annotated to post here, was taken by the Hubble Space Telescope as part of two different research projects that are studying galaxies where supernovae previously occurred. This particular galaxy is estimated to be about 192 million light years away, and is a classic example of a barred spiral.

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

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

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

What struck me about this picture however were the many smaller spiral galaxies scattered nearby and behind UGC 12295, with one face-on spiral highlighted near the top. I can count at least three or four other background spiral galaxies, all reddish in color likely because their light has been shifted to the red due to their distance.

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A confused spiral galaxy

March 6, 2023 10:34 am Robert Zimmerman

Cool image time! The picture to the right, cropped and reduced to post here, was taken by the Hubble Space Telescope and released today. From the caption:

The irregular spiral galaxy NGC 5486 hangs against a background of dim, distant galaxies in this image from the NASA/ESA Hubble Space Telescope. The tenuous disc of the galaxy is threaded through with pink wisps of star formation, which stand out from the diffuse glow of the galaxy’s bright core. While this particular galaxy has indistinct, meandering spiral arms it lies close to the much larger Pinwheel Galaxy, one of the best known examples of ‘grand design’ spiral galaxies with prominent and well-defined spiral arms. In 2006 Hubble captured an image of the Pinwheel Galaxy which was — at the time — the largest and most detailed photo of a spiral galaxy ever taken with Hubble.

This galaxy is defined I think as an irregular spiral because if you look close, you can see a very faint hint of a central bar and two large arms spiraling away at its ends. It is faint however, and might simply be caused by the human mind’s natural desire to see patterns. To my eye this galaxy could just as well be a patchy elliptical galaxy, with no arms at all.

Hubble takes a long exposure of spiral galaxy

November 7, 2022 9:12 am Robert Zimmerman

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This morning’s cool image on the right, reduced and sharpened to post here, comes courtesy of the Hubble Space Telescope.

NGC 7038 lies around 220 million light-years from Earth in the southern constellation Indus. This image portrays an especially rich and detailed view of a spiral galaxy, and exposes a huge number of distant stars and galaxies around it. That’s because it’s made from a combined 15 hours worth of Hubble time focused on NGC 7038 and collecting light. So much data indicates that this is a valuable target, and indeed, NGC 7038 has been particularly helpful to astronomers measuring distances at vast cosmic scales.

The press release focuses on how astronomers will use this data to refine the techniques they use to estimate distances to astronomical objects. However, a deep field image of this galaxy offers a wealth of other data. Note the reddish streams of dust along and between the spiral arms. This dust, as well as the bright patches in those arms likely signal star-forming regions. And I expect the details in the full resolution image, too large to make available on a webpage, would tell astronomers a lot about what is going on in the galaxy’s central regions.

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Another grand galaxy imaged by Hubble

May 26, 2022 2:30 pm Robert Zimmerman

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Cool image time! The photo to the right, reduced to post here, was released today and is one in what has become a steady string of recent and quite spectacular galaxy images produced by scientists using the Hubble Space Telescope. From the caption:

This image from NASA’s Hubble Space Telescope features the Grand Design Spiral, NGC 3631, located some 53 million light-years away in the direction of the constellation Ursa Major. The “arms” of grand design spirals appear to wind around and into the galaxy’s nucleus.

Close inspection of NGC 3631’s grand spiral arms reveals dark dust lanes and bright star-forming regions along the inner part of the spiral arms. Star formation in spirals is similar to a traffic jam on the interstate. Like cars on the highway, slower moving matter in the spiral’s disk creates a bottleneck, concentrating star-forming gas and dust along the inner part of their spiral arms. This traffic jam of matter can get so dense that it gravitationally collapses, creating new stars (here seen in bright blue-white).

This spiral follows the classic shape of these whirlpool galaxies. The Milky Way, though also a spiral, is now thought to be a barred spiral, whereby the galaxy’s whirlpool shape is distorted by a large straight bar of stars crossing its center.

Scientists also released today a second photo from Hubble of a different spiral galaxy, which you can check out here.

The spiral galaxy M91

April 15, 2022 3:38 pm Robert Zimmerman

Click for full release image.

Cool image time! The image to the right, reduced to post here, was released today by the Space Telescope Science Institute as part of a regular program using the Hubble Space Telescope to photograph galaxies.

This observation is part of an effort to build a treasure trove of astronomical data exploring the connections between young stars and the clouds of cold gas in which they form. To do this, astronomers used Hubble to obtain ultraviolet and visible observations of galaxies already seen at radio wavelengths by the ground-based Atacama Large Millimeter/submillimeter Array.

The galaxy is estimated to be about 55 million light years away, and is thought to have a supermassive black hole at its center with a mass somewhere between 9 and 38 million times the mass of the Sun.

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New analysis throws wrench in formation theory of spirals in galaxies

June 11, 2019 8:29 am Robert Zimmerman

The uncertainty of science: A new analysis of over 6000 galaxies suggests that a long-held model for the formation of spirals in galaxies is wrong.

[Edwin] Hubble’s model soon became the authoritative method of classifying spiral galaxies, and is still used widely in astronomy textbooks to this day. His key observation was that galaxies with larger bulges tended to have more tightly wound spiral arms, lending vital support to the ‘density wave’ model of spiral arm formation.

Now though, in contradiction to Hubble’s model, the new work finds no significant correlation between the sizes of the galaxy bulges and how tightly wound the spirals are. This suggests that most spirals are not static density waves after all.

Essentially, we still have no idea why spirals form in galaxies.

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Is it dark matter, or a previously unrecognized failure of Newton?

April 29, 2015 9:42 am Robert Zimmerman

Dark matter?

The uncertainty of science: Using new data gathered by the 10-meter Keck telescope in Hawaii, astronomers have found that the outer stars of elliptical galaxies exhibit the same behavior as the outer stars of spirals, suggesting once again the existence of dark matter.

One of the most important scientific discoveries of the 20th century was that the spectacular spiral galaxies, such as our own Milky Way, rotate much faster than expected, powered by [the] extra gravitational force of invisible “dark matter” as it is now called. Since this discovery 40 years ago, we have learned that this mysterious substance, which is probably an exotic elementary particle, makes up about 85 percent of the mass in the Universe, leaving only 15 percent to be the ordinary stuff encountered in our everyday lives. Dark matter is central to our understanding of how galaxies form and evolve – and is ultimately one of the reasons for the existence of life on Earth – yet we know almost nothing about it.

“The surprising finding of our study was that elliptical galaxies maintain a remarkably constant circular speed out to large distances from their centers, in the same way that spiral galaxies are already known to do,” said Cappellari. “This means that in these very different types of galaxies, stars and dark matter conspire to redistribute themselves to produce this effect, with stars dominating in the inner regions of the galaxies, and a gradual shift in the outer regions to dark matter dominance.”

What is most fascinating about this press release, however, is that it also noted that dark matter is only one explanation for the data, and that the failure of Newtonian physics at large distances, instead of dark matter, might also provide an explanation.

However, the [solution] does not come out naturally from models of dark matter, and some disturbing fine-tuning is required to explain the observations. For this reason, the [problem] even led some authors to suggest that, rather than being due to dark matter, it may be due to Newton’s law of gravity becoming progressively less accurate at large distances. Remarkably, decades after it was proposed, this alternative theory (without dark matter) still cannot be conclusively ruled out.

Physicists call this other theory MOND, for modified Newtonian dynamics. It is not a very popular theory, however, and is almost always ignored, even though it appears to work as well as dark matter to explain the motion of stars in galaxies. Instead, most scientists favor dark matter.

For this press release to mention it as suggests the new data favors it over dark matter, which would make this a significant discovery.

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