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I have been fascinated by galaxies for most of my adult life. I find it amazing that, just as we can ascertain the lifecycle of a tree by closely studying the trees in a forest, it is possible to study a sample of galaxies and understand galactic evolution.  A team of astronomers using the Gemini North Telescope have recently solved a long standing galactic mystery, namely how we get ultra-compact dwarf galaxies (UCDs to use their catchy acronym).

We are all familiar with spiral, barred-spiral and elliptical galaxies – ignoring the unclassifiable (if that’s even a word) irregular galaxy classification – but there are more. The UCD’s, which were discovered over twenty years ago, are one such lesser known classification and are among the densest stellar objects in the universe. They are more compact than most other galaxies, thought to be of the order of 200 light years across with about 100 million stars and have similar mass, but larger than star clusters.  They are almost like globular clusters but on steroids! 

The problem with them is that there is no evidence that supports why they exist! The dominant theory is that they are the nucleus of dwarf galaxies that remain after the outer layers have been stripped away. However like a walk through our forest analogy where we could see examples of trees during all stages of their life, until now, there have been no observations of this process actually taking place.

Previous searches have revealed no evidence of the transition phase so a team of astronomers have embarked on a systematic hunt for them among the Virgo Cluster of galaxies (a group of over a thousand galaxies, 5 million light years across). The international team of astronomers used the 8.1 metre Gemini North Telescope at Mauna Kea in Hawaii for their search. They first identified the galaxies they wanted to study by looking at images from the Next Generation Virgo Cluster Survey. The images were taken using the Canada-France-Hawaii Telescope and from this they identified hundreds of galaxies to observe.

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The Gemini North Telescope operated by NSF’s NOIRLab. (Credit – NOIRLab/NSF/AURA/T. Slovinský)

The galaxies they were interested in were all thought to be potential progenitor UCDs, potential because UCDs that had stars surrounding them as they were being stripped were indistinguishable from more distant galaxies. Using the Gemini North Telescope, spectroscopic observations of the target galaxies revealed accurate distance measurements so they could eliminate distant objects leaving only those in the Virgo Cluster. Among the remaining sample are dwarf galaxies with ultra compact dense cores that are representative of the progenitor objects before they lose their outer layers of stars and gas that are subsequently stripped by nearby massive galaxies. 

Furthermore and to the delight of the team, in the same study they found almost 100 objects with very extended diffuse envelopes of stars which are believed to be dwarf galaxies in the throes of losing their outer layers. As if in a text book and as postulated by the theory, they were even close to massive galaxies who very likely played a great part in their formation. Until now, the missing piece of the jigsaw had eluded discovery but it seems now, the story of ultra-compact dwarf galaxies may be complete. 

Source : Gemini North Reveals the Formation of Dense Dwarf Galaxy ‘Fossils’

The post Mystery Solved. How We Get Ultra-Compact Dwarf Galaxies appeared first on Universe Today.

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How to Get a Permit to Backpack the Teton Crest Trail

Tet19 047 Me on Teton Crest Trail copy cropped jpg

By
Michael Lanza

For
backpackers, the Teton Crest Trail really delivers it all: beautiful lakes,
creeks, and waterfalls, high passes with sweeping vistas, endless meadows of
vibrant wildflowers, a good chance of seeing wildlife like elk and moose, some
of the best campsites you will ever pitch a tent in, and mind-boggling scenery
just about every step of the way. And it’s a relatively beginner-friendly trip
of 40 miles or less, which most people can hike in four to five days.

No wonder it’s so enormously popular—and there’s so much competition for backcountry permits.

In this story, I will offer tips on how to maximize your chances of getting a permit to backpack the Teton Crest Trail, sharing expertise I’ve acquired from more than 20 trips in the Tetons and several on the Teton Crest Trail over more than three decades, including the 10 years I spent as Northwest Editor of Backpacker magazine and even longer running this blog.

Tet19 047 Me on Teton Crest Trail copy cropped 1 jpg
Hi, I’m Michael Lanza, creator of The Big Outside. Click here to sign up for my FREE email newsletter. Join The Big Outside to get full access to all of my blog’s stories. Click here for my e-guides to classic backpacking trips. Click here to learn how I can help you plan your next trip.

Lake Solitude, North Fork Cascade Canyon, Grand Teton National Park.
” data-image-caption=”Lake Solitude in the North Fork of Cascade Canyon, Grand Teton National Park. Click photo for my e-guide “The Complete Guide to Backpacking the Teton Crest Trail.”
” data-medium-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?fit=300%2C200&ssl=1″ data-large-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?fit=900%2C600&ssl=1″ src=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=900%2C600&ssl=1″ alt=”Lake Solitude, North Fork Cascade Canyon, Grand Teton National Park.” class=”wp-image-36414″ srcset=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=1024%2C683&ssl=1 1024w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=300%2C200&ssl=1 300w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=768%2C512&ssl=1 768w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?resize=1080%2C720&ssl=1 1080w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-095-Lake-Solitude-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P..jpg?w=1200&ssl=1 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />Lake Solitude in the North Fork of Cascade Canyon, Grand Teton National Park. Click photo for my e-guide “The Complete Guide to Backpacking the Teton Crest Trail.”

See my story from my most-recent trip on it, “A Wonderful Obsession: Backpacking the Teton Crest Trail,” which requires a paid subscription to The Big Outside to read in full, including basic information on planning a TCT backpacking trip. For much more information and expert tips on planning this trip, get my top-selling e-guide “The Complete Guide to Backpacking the Teton Crest Trail in Grand Teton National Park.”

I’ve also helped many readers plan a backpacking trip in the Tetons and elsewhere, answering all of their questions and customizing an itinerary ideal for them. See my Custom Trip Planning page to learn how
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Eris Could be Slushier Than Pluto

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In 2005, astronomer Mike Brown and his colleagues Chad Trujillo and David Rabinowitz announced the discovery of a previously unknown planetoid in the Kuiper Belt beyond Neptune’s orbit. The team named this object Eris after the Greek personification of strife and discord, which was assigned by the IAU a year later. Along with Haumea and Makemake, which they similarly observed in 2004 and 2005 (respectively), this object led to the “Great Planet Debate,” which continues to this day. Meanwhile, astronomers have continued to study the Trans-Neptunian region to learn more about these objects.

While subsequent observations have allowed astronomers to get a better idea of Eris’ size and mass, there are many unresolved questions about the structure of this “dwarf planet” and how it compares to Pluto. In a recent study, Mike Brown and University of California Santa Cruz professor Francis Nimmo presented a series of models based on new mass estimates for Eris’ moon Dysnomia. According to their results, Eris is likely differentiated into a convecting icy shell and rocky core, which sets it apart from Pluto’s conductive shell.

Their paper, “The internal structure of Eris inferred from its spin and orbit evolution,” recently appeared in the journal Science Advances. The research began while Nimmo was visiting Professor Brown at Caltech and realized that some of his previously-unpublished data could help reveal information about the properties of Eris. At present, we know that Eris is about the same size and mass as Pluto and has a highly eccentric orbit around our Sun, ranging from 38.271 AU at perihelion to 97.457 AU at aphelion. This is almost twice as eccentric as Pluto’s orbit and roughly 50% farther from the Sun.

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Comparison between the eight largest TNOs with Earth (all to scale). Credit: NASA/Lexicon

For several months, Brown and Nimmo worked on models of Eris that incorporated two key pieces of information. The first had to do with Eris’ only known satellite, Dysnomia, and how the two bodies always face the same way toward each other. “That happens because the big planet gets spun down by the tides that the little moon raises on it,” said Nimmo in a recent UCSC press release. “The bigger the moon is, the faster the planet spins down. And so as soon as you know that, then you can actually start to do real calculations.”

Astronomers can use the spin and orbital characteristics of planets and their moons to infer certain properties, like their internal structures. But until recently, scientists did not have estimates on Dysnomia’s size, mass, and density. Luckily, Brown and his colleague Bryan J. Butler – a researcher at the National Radio Astronomy Observatory (NRAO) – recently conducted observations of Dysnomia and Eris (and Orcus and its satellite Vanth) using the Atacama Large Millimeter-submillimeter Array (ALMA). Based on their findings, published in The Planetary Science Journal, Dysnomia has a diameter of about 615 km (382 mi) and Dysnomia and Eris have a mass ratio of 0.0085.

This upper mass limit provided the second crucial piece of information, which concerned Eris’ internal structure. The main result of Brown and Nimmo’s model (but did not expect) is that Eris is surprisingly dissipative, a concept in thermodynamics where a system operates out of equilibrium. From this, they determined that Eris has a rocky core surrounded by a layer of ice and a crust that is likely convecting. “The rock contains radioactive elements, and those produce heat,” Nimmo said. “And then that heat has to get out somehow. So as the heat escapes, it drives this slow churning in the ice.” 

This sets it apart from Pluto, which has a conducting shell, as revealed by the New Horizon mission. Brown and Nimmo hope that more exact measurements of Dysnomia’s mass will be available in the near future, as well as additional data about the shape of Eris. Because of its distance, Eris appears as a single pixel of light, while Dysnomia is visible as a faint speck next to it (see below). Therefore, astronomers must monitor Eris as it passes in front of background stars to reconstruct its shape. This is similar to the Transit Method astronomers use to detect exoplanets and constrain their sizes.

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Hubble is Offline Because of a Problem with one of its Gyros

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The rich flow of scientific data—and stunning images—that comes from the Hubble Space Telescope is being interrupted by gyro problems. One of the telescope’s three remaining gyros gave faulty readings, and the Hubble automatically entered safe mode. In safe mode, science operations are suspended.

Without gyros, the Hubble can’t orient itself properly. Gyros measure the telescope’s turn rate and help the telescope know where it’s pointed. They’re part of the system that keeps the space telescope pointed in the right direction. There’s no indication of any problems with Hubble’s instruments, like its Wide-Field Camera 3 or its Advanced Camera for Surveys.

This all began on November 19th when Hubble went into safe mode. Engineers recovered the telescope, and regular science operations resumed the following day. However, the unstable gyro caused problems again, and the space telescope suspended science operations again on the 21st. It was recovered again, then went back into safe mode on November 23rd. That’s where things stand now.

NASA is working to resume science operations of the Hubble Space Telescope after it entered safe mode Nov. 23 due to an ongoing gyroscope issue. Hubble’s instruments are stable, and the telescope is in good health: https://t.co/QOdJJ9WjYh pic.twitter.com/URRHYV3Le8

— Hubble (@NASAHubble) November 29, 2023

The Hubble was launched with six original gyros, but they failed fairly rapidly. During its last shuttle servicing mission in 2009, the Hubble received six new gyros. Three of them were the older type that failed fairly quickly, and three were new ones. The three older ones from 2009 have failed, and Hubble has three remaining gyros, and all of them have a more modern design. It can operate with a single functioning gyro, though it’s less efficient.

This image shows astronaut Mike Massimino during Service Mission 4 to the Hubble in 2009. Astronaut Mike Good is in the background. During SM-4, Hubble received new gyroscopes, as well as two new scientific instruments – the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Image Credit: NASA
This image shows astronaut Mike Massimino during Service Mission 4 to the Hubble in 2009. Astronaut Mike Good is in the background. During SM-4, Hubble received new gyroscopes, as well as two new scientific instruments – the Cosmic Origins Spectrograph (COS) and Wide Field Camera 3 (WFC3). Image Credit: NASA

Each gyro is a small cylinder filled with fluid. Inside the fluid, an internal float spins thousands of times per second. The original six gyros and three of the 2009 replacements contained bromine in the fluid. The bromine ate away at the gyros, causing their eventual demise.

One of the Hubble's gyros. Older ones had bromine in their interior fluid, which ate away at the gyros, causing their demise. Image Credit: NASA
One of the Hubble’s gyros. Older ones had bromine in their interior fluid, which ate away at the gyros, causing their demise. Image Credit: NASA

This isn’t the first time failing gyros have caused a shutdown in Hubble’s science operations. The preceding incident happened in 2018. At that time, Ken Sembach was the Director of the Space Telescope Science Institute (STScI.) In an interview, he expressed some frustration, telling Business Insider, “We’ve had some issues with this gyro in the past, and we’ve got some possible leads on the current problem. But the thing that’s been clear on Hubble is that these gyros all have a mind of their own. I don’t think anybody really knows what’s going on with it right now.”

The gyros are just part of the system that keeps Hubble pointed where astronomers want it pointed. The system also includes reaction wheels and fine guidance sensors
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