Tag: astronomy

XRISM X-ray space telescope functioning despite closed “aperture door”

9:50 am

XRISM, a joint X-ray space telescope built by NASA and Japan’s space agency JAXA, is collecting data despite the failure on one instrument of an aperture door to open.

In January, project scientists said that XRISM was working well except for an aperture door, also called a gate valve, for the Dewar on its imaging instrument, Resolve, which failed to open. The instrument can still operate with the door closed, although the door, made of beryllium, does attenuate some X-rays at lower energies.

At the time, efforts were underway to try and open the gate valve. However, speaking at a May 7 meeting of the National Academies’ Board on Physics and Astronomy, Mark Clampin, director of NASA’s astrophysics division, said those efforts were on hold for the next year and a half.

Instead, the science team decided to proceed with science operations, since the telescope has two other working instruments, and can get data even from this hindered third.

XRISM is a replacement of a previous JAXA X-ray telescope that launched in 2016 but failed immediately.

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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
Click for original image.

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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TESS resumes science operations

9:26 am

Engineers have corrected the issue that put the space telescope TESS into safe mode on April 8, 2024 and have resumed science operations.

The operations team determined this latest safe mode was triggered by a failure to properly unload momentum from the spacecraft’s reaction wheels, a routine activity needed to keep the satellite properly oriented when making observations. The propulsion system, which enables this momentum transfer, had not been successfully repressurized following a prior safe mode event April 8. The team has corrected this, allowing the mission to return to normal science operations. The cause of the April 8 safe mode event remains under investigation.

As for that April 8th safe mode, though engineers were able to return the spacecraft to normal operations after about a week, that they still do not know what caused it remains a concern.

TESS takes high resolution survey images of 93% of the sky about once per month. By comparing the data from each scan, scientists have discovered so far more than 300 transiting exoplanets as well as many supernovae and other phenomenon related to variable stars.

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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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Hubble out of safe mode and resumed science observations

8:43 am

According to the Hubble website, engineers have corrected the gyro issue that put the Hubble Space Telescope into safe mode on April 23, 2024.

On April 30, 2024, NASA announced it restored the agency’s Hubble Space Telescope to science operations April 29. The spacecraft is in good health and once again operating using all three of its gyros. All of Hubble’s instruments are online, and the spacecraft has resumed taking science observations.

No other information was released. The safe mode was initiated by faulty readings from one of those gyros. Was the problem in the gyro itself, or were the readings merely incorrect? This matters because when one of those gyros finally fails, the telescope will go to one-gyro mode, saving its second gyro in reserve. At that point Hubble will no longer be able to take sharp images, though it will still be able to some science.

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Webb maps the global temperature and water vapor of a hot exoplanet

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The uncertainty of science: Using detailed infrared data from the Webb Space Telescope, scientists have mapped the temperature swings and atmospheric water vapor across the entire global of a tidally locked “hot Jupiter” exoplanet about 284 light years away that orbits its star every 19.5 hours.

The team used Webb’s MIRI (Mid-Infrared Instrument) to measure light from the WASP-43 system every 10 seconds for more than 24 hours. “By observing over an entire orbit, we were able to calculate the temperature of different sides of the planet as they rotate into view,” explained Bell. “From that, we could construct a rough map of temperature across the planet.”

The measurements show that the dayside has an average temperature of nearly 2,300 degrees Fahrenheit (1,250 degrees Celsius) – hot enough to forge iron. Meanwhile, the nightside is significantly cooler at 1,100 degrees Fahrenheit (600 degrees Celsius). The data also helps locate the hottest spot on the planet (the “hotspot”), which is shifted slightly eastward from the point that receives the most stellar radiation, where the star is highest in the planet’s sky. This shift occurs because of supersonic winds, which move heated air eastward.

…To interpret the map, the team used complex 3D atmospheric models like those used to understand weather and climate on Earth. The analysis shows that the nightside is probably covered in a thick, high layer of clouds that prevent some of the infrared light from escaping to space. As a result, the nightside – while very hot – looks dimmer and cooler than it would if there were no clouds.

The data also found water vapor on both the day and night sides of the exoplanet, but surprisingly no evidence of methane, suggesting that atmosphere has high winds exceeding 5,000 miles per hour that mixes that atmosphere globally. Any methane that was expected to exist on the night side gets blown to the day side where the heat destroys it.

This data, while excellent, is also very coase and even more uncertain. While Webb can get good infrared spectroscopy from almost 300 light years away, we must take the interpretations of that data with great skepticism.

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Webb takes an infrared look at the mane of the Horsehead Nebula

10:01 am

Context images
Click for original image.

The mane of the Horsehead Nebula, seen in infrared
Click for original image.

The cool infrared image to the right, cropped, reduced, and sharpened to post here, was taken by the Webb Space Telescope and released today. The three pictures above provide the context, with the rectangle inside the rightmost image indicated the area covered by the close-up to the right.

Webb’s new images show part of the sky in the constellation Orion (The Hunter), in the western side of a dense region known as the Orion B molecular cloud. Rising from turbulent waves of dust and gas is the Horsehead Nebula, otherwise known as Barnard 33, which resides roughly 1,300 light-years away.

The nebula formed from a collapsing interstellar cloud of material, and glows because it is illuminated by a nearby hot star. The gas clouds surrounding the Horsehead have already dissipated, but the jutting pillar is made of thick clumps of material and therefore is harder to erode. Astronomers estimate that the Horsehead has about five million years left before it too disintegrates. Webb’s new view focuses on the illuminated edge of the top of the nebula’s distinctive dust and gas structure.

In the close-up, note the many distant tiny galaxies, both above the mane as well as glowing throught it.

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Movies of two supernovae remnants produced from two decades of Chandra X-ray images

9:51 am

Using more than two decades of data from the Chandra X-ray Observatory, scientists have created two movies of the supernovae remnants the Crab nebula and Cassiopeia A.

I have embedded those movies below. From the press release:

Over 22 years, Chandra has taken many observations of the Crab Nebula. With this long runtime, astronomers see clear changes in both the ring and the jets in the new movie. Previous Chandra movies showed images taken from much shorter time periods — a 5-month period between 2000 and 2001 and over 7 months between 2010 and 2011 for another. The longer timeframe highlights mesmerizing fluctuations, including whip-like variations in the X-ray jet that are only seen in this much longer movie. A new set of Chandra observations will be conducted later this year to follow changes in the jet since the last Chandra data was obtained in early 2022.

…Cassiopeia A (Cas A for short) is the remains of a supernova that is estimated to have exploded about 340 years ago in Earth’s sky. While other Chandra movies of Cas A have previously been released, including one with data extending from 2000 to 2013, this new movie is substantially longer featuring data from 2000 through to 2019.

» Read more

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Hubble celebrates 34 years in orbit with a new photo of the Little Dumbbell Nebula

9:53 am

The Little Dumbbell Nebula
Click for original image.

Cool image time! To celebrate the 34th anniversay of its launch in 1990, astronomers have used the Hubble Space Telescope to take a new photo of the Little Dumbbell Nebula (also known as M76), located about 3,400 light years away and one of the most well-known planetary nebulae in the sky.

That picture is to the right, cropped, reduced, and sharpened to post here. From the caption:

M76 is composed of a ring, seen edge-on as the central bar structure, and two lobes on either opening of the ring. Before the star burned out, it ejected the ring of gas and dust. The ring was probably sculpted by the effects of the star that once had a binary companion star. This sloughed off material created a thick disk of dust and gas along the plane of the companion’s orbit. The hypothetical companion star isn’t seen in the Hubble image, and so it could have been later swallowed by the central star. The disk would be forensic evidence for that stellar cannibalism.

The primary star is collapsing to form a white dwarf. It is one of the hottest stellar remnants known at a scorching 250,000 degrees Fahrenheit, 24 times our Sun’s surface temperature. 
The sizzling white dwarf can be seen as a pinpoint in the center of the nebula. A star visible in projection beneath it is not part of the nebula.



Pinched off by the disk, two lobes of hot gas are escaping from the top and bottom of the “belt,” along the star’s rotation axis that is perpendicular to the disk. They are being propelled by the hurricane-like outflow of material from the dying star, tearing across space at two million miles per hour.

Since launch Hubble has made 1.6 million observations of over 53,000 astronomical objects, and continues to be in high demand by astronomers, with only one request in six able to get time on the telescope. Not surprisingly, almost all of Hubble’s biggest discoveries were unexpected. Its future right now rests with its last three working gyroscopes used to orient it precisely. When one more fails, it will go to one-gyro mode, which will limit the precision of that orientation significantly. At that point the sharpness of the telescope’s imagery will sadly decline.

The only comparable orbital optical telescope now planned is China’s Xuntian optical telescope, scheduled for launch next year. It will fly in formation with the Tiangong-3 space station, allowing astronauts to periodically do maintenance missions to it. As I noted many times previously, American astronomers better start learning Chinese, assuming China even allows them access. Nor will these American astronomers have a right to complain, as it was their decision to not build a Hubble replacement, in their 2000, 2010, and 2020 decadal reports.

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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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Analysis of Io’s atmosphere suggests it has been volcanically active for its entire 4+ billion year history

9:34 am

By analysizing the isotobes in Io’s atmosphere, scientists now believe that it has been volcanically active since its initial formation at the birth of the solar system 4.5 billion years ago.

de Kleer et al. found that both elements [ sulfer- and chlorine-bearing molecules] are highly enriched in heavy isotopes compared to average Solar System values due to the loss of lighter isotopes from the upper atmosphere as material is continuously recycled between Io’s interior and atmosphere. The findings indicate that Io has lost 94% to 99% of the sulfur that undergoes this outgassing and recycling process. According to the authors, this would require Io to have had its current level of volcanic activity for its entire lifetime.

This data suggests that Io, as well as Jupter’s other three large Galilean moons (Europa, Calisto, and Ganymeded) have been in their present orbits since their formation 4.5 billion years ago. It also means that, while Io’s geological history keeps getting wiped out by its volcanic activity, the other three contain detailed geological records of the solar system’s entire history. Combine that with the geological data we will eventually get from Mars, it appears that we shall someday be able to document that history far beyond anything expected.

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TESS has resumed science operations

9:15 am

Engineers have successfully returned TESS to full science operations, without providing as yet any explanaton as to why on April 8, 2024 it went into safe mode or what they did to fix the issue.

The Aprill 11 press release announcing the safe mode had only mentioned that the shut down had occurred “during scheduled engineering activities.” The lack of information continues to suggest that someone did an “Oops!” during those activities, and NASA is too embarassed to reveal that fact.

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Using Gaia data scientists discover the heaviest stellar black hole ever found

10:30 am

In digging into the precise motion data from the Gaia space telescope scientists have discovered the Milky Way’s heaviest stellar-sized black hole, with a mass thirty-three times the mass of our Sun.

Stellar black holes are formed from the collapse of massive stars and the ones previously identified in the Milky Way are on average about 10 times as massive as the Sun. Even the next most massive stellar black hole known in our galaxy, Cygnus X-1, only reaches 21 solar masses, making this new 33-solar-mass observation exceptional.

Remarkably, this black hole is also extremely close to us — at a mere 2000 light-years away in the constellation Aquila, it is the second-closest known black hole to Earth.

The only known black hole inside the Milky Way that is larger is Sagittarius A* (pronounced A-star), the supermassive central black hole at the galaxy’s center and weighing over four million solar masses. That creature is a very different thing, as it involves the long term evolution of the galaxy itself. Stellar-sized black holes only involve the death of a single star, with possible additions from a handful of others.

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TESS in safe mode

9:43 am

NASA today revealed that on April 8, 2024 its TESS space telescope went into safe mode, for reasons that are not yet understood.

NASA’s TESS (Transiting Exoplanet Survey Satellite) entered into safe mode April 8, temporarily interrupting science observations. The team is investigating the root cause of the safe mode, which occurred during scheduled engineering activities. The satellite itself remains in good health.

The spacecraft itself remains healthy and they expect to resume science operations “in the coming days.”

That safe mode occurred while “scheduled engineering activities” were ongoing suggests that the two are linked. The lack of any details from NASA further suggests that someone did a “oops!” during those activities, and they are now scrambling to fix things.

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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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Lunar Reconnaissance Orbiter snaps a smeared image of South Korea’s Danuri lunar obiter

10:04 am

Danuri as seen by LRO
Click for original image.

Cool image time! On March 5 to March 6, 2024, the orbits of NASA’s Lunar Reconnaissance Orbiter (LRO) and South Korea’s Danuri orbiter had three close approaches, during which LRO had a chance to snap pictures of Danuri as it zipped by in the opposite direction.

The first image is to the right, cropped but expanded to post here.

The flight paths of the two vehicles were nearly parallel but in opposite directions, resulting in extreme relative velocity. The LROC NAC exposure time was very short, only 0.338 milliseconds. But still, Danuri was smeared by a factor greater than 10x in the downtrack direction.

…On the first opportunity, LRO was slewed 43 degrees to capture Danuri from a distance of 5.0 kilometers

Of the three pictures taken, this one appears the best. In all three cases, the fast relative speed was too fast for the camera shutter, so that Danuri’s image was smeared as you see.

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Today’s eclipse

9:49 am

The next eclipses to cross the U.S.
Map by Michael Zeiler (GreatAmericanEclipse.com). Click for original.

Today a solar eclipse will cross some of the most populated areas of Mexixo, the United States, and Canada, as shown on the map to the right.

We shall not see such an event in North America again until 2046, and that will only cover a small part of the Pacific northwest. If you have never seen such an event, get your eclipse glasses (essential if you don’t want to go blind), take some time off of work, and go see it today. This link from Sky & Telescope covers about everything you need to know.

The experience is very hard to describe, though I tried when Diane and I traveled to South Bend, Idaho, in 2017 to experience that eclipse. As I wrote,

Totality was amazing. I was amazed by two things. First, how quiet it became. There were about hundred people scattered about the hotel lawn, with dogs and kids playing around. The hotel manager’s husband set up speakers for music and to make announcements, but when totality arrived he played nothing. People stopped talking. A hush fell over everything. Moreover, I think we somehow imagine a subconscious roar from the full sun. Covered as it was, with its soft corona gleaming gently around it, it suddenly seemed still.

Secondly, the amazing unlikeliness of the Moon being at just the right distance and size to periodically cause this event seemed almost miraculous. Watching it happen drove this point home to me. And since eclipses themselves have been a critical event in the intellectual development of humanity, helping to drive learning and our understanding of the universe, it truly makes me wonder at the majesty of it. I do not believe in any particular religion or their rituals (though I consider the Bible, the Old Testament especially, to be a very good manual for creating a good life and society), but I do not deny the existence of a higher power. Something made this place, and set it up in this wonderous way. Today’s eclipse only served to demonstrate this fact to me again.

I am sure your impressions will be unique to you.

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Engineers confirm IXPE is fixed and resuming science observations

10:00 am

Engineers have now confirmed the software fix they sent to the IXPE space telescope on March 26, 2024 has worked, and have taken the telescope out of safe mode so that it can resume science observations.

The IXPE mission is now observing a new transient X-ray source – Swift J1727.8–161 – a candidate accreting black hole. The source has recently begun producing jets of material moving at a fraction of the speed of light. The IXPE observations will help to understand accretion onto black holes, including potentially revealing how the relativistic jets are formed.

The telescope observes the universe in X-rays, but does so by observing its polarization. This approach provides information not seen in direct observations.

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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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The remnant of the supernova from 1181, as seen in multiple wavelengths

9:44 am

Supernova remnant as seen in multiple wavelengths
Click for original image.

Using a number of different telescopes and observing in many wavelengths outside the visible spectrum, astronomers have produced a new composite image of the remnant of a supernova that was detected in the year 1181 and remained visible to the naked eye for about six months.

That composite picture is to the right, cropped and reduced to post here. From the press release:

X-ray observations by ESA’s XMM-Newton (blue) show the full extent of the nebula and NASA’s Chandra X-ray Observatory (cyan) pinpoints its central source. The nebula is barely visible in optical light but shines bright in infrared light, collected by NASA’s Wide-field Infrared Space Explorer (red and pink). Interestingly, the radial structure in the image consists of heated sulfur that glows in visible light, observed with the ground-based Hiltner 2.4 m telescope at the MDM Observatory (green) in Arizona, USA, as do the stars in the background by Pan-STARRS (white) in Hawaii, USA.

Because the remnant is so dim in visible light, it has taken years of searching to locate it.

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The spiraling magnetic field surrounding the Milky Way’s central supermassive black hole

9:19 am

The magnetic field lines surrounding Sagittarius A*
Click for original image.

Astronomers have now produced the first detailed image of polarized light surrounding the Milky Way’s central supermassive black hole, dubbed Sagittarius A* (pronounced “Sagittarius A-star”) which in turn maps out the spiraling field lines of that black hole’s magnetic field.

The image to the right, reduced to post here, shows that image. From the press release:

“What we’re seeing now is that there are strong, twisted, and organized magnetic fields near the black hole at the center of the Milky Way galaxy,” said Sara Issaoun, CfA NASA Hubble Fellowship Program Einstein Fellow, Smithsonian Astrophysical Observatory (SAO) astrophysicist, and co-lead of the project. “Along with Sgr A* having a strikingly similar polarization structure to that seen in the much larger and more powerful M87* black hole, we’ve learned that strong and ordered magnetic fields are critical to how black holes interact with the gas and matter around them.”

Light is an oscillating, or moving, electromagnetic wave that allows us to see objects. Sometimes, light oscillates in a preferred orientation, and we call it “polarized.” Although polarized light surrounds us, to human eyes it is indistinguishable from “normal” light. In the plasma around these black holes, particles whirling around magnetic field lines impart a polarization pattern perpendicular to the field. This allows astronomers to see in increasingly vivid detail what’s happening in black hole regions and map their magnetic field lines.

Despite this similarlity, it still remains a mystery why the much larger M87 black hole is very active while Sagittarius A’ remains generally quiet.

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Engineers resolve issue on IXPE space telescope

9:01 am

Engineers have resolved the issue on the IXPE (Imaging X-ray Polarimetry Explorer) space telescope that was jumbling the data it was sending to Earth, and expect to return it to full science operations shortly.

On March 26, using procedures developed following that previous interruption, the team initiated a spacecraft avionics reset to address the issue, which put IXPE into a planned safe mode. The team has confirmed that IXPE is once again transmitting valid telemetry data and is now working to resume science operations, in as rapid and safe a manner as possible. The spacecraft is in good health.

The “previous interruption” was in 2023. In both cases it appears that simply rebooting the telescope’s software fixed the problem.

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The tangled view of astronomers

11:06 am

A protostar in formation
Click for original image.

The uncertainty of science: 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 young stars surrounded by an edge-on dust disk. From the caption:

FS Tau is a multi-star system made up of FS Tau A, the bright star-like object near the middle of the image, and FS Tau B (Haro 6-5B), the bright object to the far right that is partially obscured by a dark, vertical lane of dust. The young objects are surrounded by softly illuminated gas and dust of this stellar nursery. The system is only about 2.8 million years old, very young for a star system. Our Sun, by contrast, is about 4.6 billion years old.

The blue lines on either side of that vertical dust lane are jets moving out from FS Tau B. The caption says their asymetrical lengths are likely due to ” mass is being expelled from the object at different rates,” but it just as easily be caused by the angle in which we see this object, making the nearer jet seem longer than the one behind.

That astronomers cannot move around such an object and see it from many angles explains the headline of this post. We can only see astronomical objects from one angle, and when they are complex objects such as this one, a large part of the research problem is disentangling the shapes we see into a coherent picture. Spectroscopy helps a lot, as it provides information about the speed and direction of different parts of the object, but even this can be enormously complicated and difficult to interpret.

Remember these facts when you read news reports about astronomical research. No matter how certain the press release sounds, its certainty is always tempered by many unknowns, some very pedestrian but fundamental.

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Citizen scientist project discovers 16 active asteroids

10:39 am

A project that has enlisted approximately 8,300 ordinary citizens to review more than 430,000 photos taken by a telescope in Chile has discovered sixteen asteroids that produce comae and tails like comets.

Identifying and tracking active asteroids whose activity specifically appears to be due to the sublimation of ice – known as main-belt comets – is a particular interest of the project team, as it is an essential part of understanding the abundance and distribution of volatile material like ice in the Solar System.

…The project, utilizing publicly available Dark Energy Camera (DECam) data from the Victor M. Blanco telescope in Chile, involved the examination of more than 430,000 images of known minor planets by 8,300 volunteers, where images identified by citizen scientists as being likely to contain active asteroids were then passed on to the science team for confirmation and additional analysis.

You can read the research paper here. If you want to participate, the Active Asteroids project is still on-going, and can be accessed here.

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A relatively dim star is expected to become one of the brightest in the sky later this year

9:49 am

As it has done twice before at intervals of 80 years, a relatively dim star is expected to go nova later this year, becoming for a short time one of the brightest stars in the sky.

Located in the Northern Crown constellation, T Coronae Borealis (T CrB) is a pretty average looking star, most of the time. With a brightness of about magnitude +10, it’s right on the limits of what you could see with a pair of binoculars, and even if you do go looking there’s not much to see.

At least, that’s the case for about 79 out of 80 years. But on that 80th year, the star suddenly brightens drastically up to around magnitude +2, which puts it on par with the north star Polaris. That makes it one of the brightest stars in the night sky, easily visible with the naked eye even when washed out by city lights. This once-in-a-lifetime outburst last occurred in 1946, and before that 1866.

And lucky for stargazers, T CrB seems to be about two years ahead of schedule, with astronomers predicting it will flare up again between March and September 2024. It’ll appear as a bright ‘new’ star for a few days with the naked eye, and a little over a week with binoculars, before it settles down again for another few decades. Astronomers noticed last year that T CrB had started to dim, which data from 1945 showed preceded the last brightening event.

The star is actually a binary, made up of a white dwarf and a red giant. The white dwarf is pulling material from the red giant, and as that new material piles up, it eventually gathers enough mass to go critical and produce a thermonuclear explosion. The result is a nova, a smaller version of a supernova that unlike supernovae occurs repeatedly.

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ESA: Euclid vision cleared after being fogged by ground ice, after launch

9:13 am

The European Space Agency (ESA) today announced that engineers have successfully “de-iced” the optics of its new Euclid space telescope that developed after it was launched in July 2023.

It was always expected that water could gradually build up and contaminate Euclid’s vision, as it is very difficult to build and launch a spacecraft from Earth without some of the water in our planet’s atmosphere creeping into it. For this reason, there was an ‘outgassing campaign’ shortly after launch where the telescope was warmed up by onboard heaters and also partially exposed to the Sun, sublimating most of the water molecules present at launch on or very near Euclid’s surfaces. A considerable fraction, however, has survived, by being absorbed in the multi-layer insulation, and is now being slowly released in the vacuum of space.

After a huge amount of research – including lab studies into how minuscule layers of ice on mirror surfaces scatter and reflect light – and months of calibrations in space, the team determined that several layers of water molecules are likely frozen onto mirrors in Euclid’s optics. Likely just a few to few tens of nanometres thick – equivalent to the width of a strand of DNA – it’s a remarkable testament to the mission’s sensitivity that it is detecting such tiny amounts of ice.

While Euclid’s observations and science continue, teams have come up with a plan to understand where the ice is in the optical system and mitigate its impact now and in the future, if it continues to accumulate.

It appears this new process has worked, according to a short update at the link.

Normally spacecraft are vented both on the ground during thermal testing, as well as when they reach orbit. It appears some of these normal procedures were either insufficient for Euclid’s needs, or threatened its optics if done as usual. This press release suggests that Euclid required very targeted venting processes that would not harm its sensitive optics, and that the procedures have worked.

I must admit I am suspicious of these claims. During development and after launch Euclid has had a number of problems. First, back in 2017 the NASA instrument on the telescope had to be completely rebuilt when it was found to be defective. Second, after launch engineers discovered unexpected light leaks on the mirror that now limit where it can look. Third, the telescope required a software patch to fix its pointing system, which was confusing cosmic rays for guide stars, causing it to shift positions randomly.

I can’t help wondering if this icing on the mirrors was also due, not to actual planning as suggested by ESA’s press release, but to poor ground testing and engineering that missed what is a common problem on spacecraft and thus required a post-launch improvised fix. I admit I might be wrong, but I still wonder.

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Gehrels Swift space telescope now in safe mode

9:33 am

The Gehrels Swift space telescope, used to get real time observations of gamma ray bursts and other high energy deep space events, is presently in safe mode due to the failure of one of its three gyroscopes.

On March 15, NASA’s Neil Gehrels Swift Observatory entered into safe mode, temporarily suspending science operations due to degrading performance from one of its three gyroscopes (gyros), which are used to point the observatory for making observations. The rest of the spacecraft remains in good health.

Swift is designed to successfully operate without one of its gyros if necessary; however, a software update is required. The team is working on the flight software update that would permit the spacecraft to continue science operations using its two remaining gyros.

The telescope has been operating in orbit for nearly twenty years, far longer than originally planned. Its observations were crucial in discovering that gamma ray bursts occur at vast distances and involve either the core collapse of a star or the merger of two neutron stars.

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Scientists: DART impact of Dimorphos changed its orbit and reshaped the asteroid

9:18 am

Dimorphos shape change
Click for original graphic.

According to a new study, the DART impact of Dimorphos in September 2022 not only shortened its orbit around the larger asteroid Didymos, it reshaped the asteroid itself, warping its widest point sideways from its equator.

You can read the paper here.

More important, the scientists found that the changes evolved over time.

Over the following weeks, the asteroid’s orbital period continued to shorten as Dimorphos lost more rocky material to space, finally settling at 11 hours, 22 minutes, and 3 seconds per orbit – 33 minutes and 15 seconds less time than before impact. This calculation is accurate to within 1 ½ seconds, Naidu said. Dimorphos now has a mean orbital distance from Didymos of about 3,780 feet (1,152 meters) – about 120 feet (37 meters) closer than before impact.

Similarly, the reshaping of the asteroid into its present shape took time. As the scientists noted in their conclusion, “it takes time for a binary system to settle after a kinetic impact event.”

Because of Dimorphus’s rubble pile nature, its shape and orbit should continue to evolve over the coming decades, as more of the ejecta from the impact slowly falls back onto its surface and the asteroid surface adjusts over time. This in turn should also effect the orbit, though by only very tiny amounts.

I continue to wonder if the entire solar orbit of this asteroid binary system was impacted at all by these changes. Any changes would likely be tiny, but it is important to know to see if such an impact can actually do such a thing. To find out will take several more years, as ground telescopes continue to track the asteroid.

In October 2024 the European probe Hera will launch on a mission to this asteroid binary, with its arrival expected in December 2026. At that time we will get a much better look at both asteroids and how the impact affected them.

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Betelgeuse dimming again

10:00 am

Betelqeuse
An optical image of Betelgeuse taken in 2017 by a ground-based
telescope, showing its not unusual aspherical shape.
Click for original image.

It appears that the red giant star Betelgeuse is once again dimming, as it did in 2019-2020.

Betelgeuse, located in Orion’s right shoulder, ordinarily shines at magnitude +0.4, a close match to neighboring Procyon in Canis Minor. But since late January it’s lost some of its luster — at least a third of a magnitude’s worth. That may not sound like much especially given the star’s variable nature, but the red supergiant star is currently the faintest it’s been in the past two years.

Betelgeuse is less like a stable star and more like a gasbag in weightlessness, its shape bouncing in and out as convection bubbles from within push their way to the surface. In some cases, as in 2019-2020, a burst of a bubble releases dust and material, which scientists believe acted to block the star’s light at that time. The dimming now could be for the same reason. Or it could be because the star’s brightness is fundamentally variable. For years it reliably pulsed every 400 days, though that variation pattern now seems to have vanished since 2020.

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