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The Hyades star cluster is only about 153 light-years away. At that short distance away, it’s visible with the unaided eye in the constellation Taurus. Its proximity gives professional astronomers an easier time observing it than many other objects of interest. Hyades contains hundreds of stars with similar ages—about 625 million years—similar metallicities and similar motions through space.

But something’s missing from the Hyades cluster: white dwarfs. There’s an apparent lack of them, with only eight of them in the cluster’s core. Where did they go?

The Hyades Cluster is pretty unremarkable. Studying it creates a benchmark in astronomers’ understanding of star clusters. But it does have at least one wrinkle, and that’s its lack of white dwarfs. It’s a stumbling block in understanding Hyades. However, a new study found one that was ejected from the cluster. And it’s an ultra-massive white dwarf, one that nudges up against the mass limit for this type of stellar remnant. How does it fit in?

The new research is titled “An Extremely Massive White Dwarf Escaped From the Hyades Star Cluster.” It’s been submitted to The Astrophysical Journal for publication, and the lead author is David Miller. Miller is from the Department of Physics and Astronomy at the University of British Columbia.

Open clusters like Hyades are only loosely bound, and over time, they lose stars through interactions with gas clouds, other clusters, and between cluster members. Miller and his co-researchers examined the lack of white dwarfs in Hyades as a means to reconstruct the Hyades cluster. If they can identify stars that have been evicted, especially white dwarfs in this case, they can piece together the cluster’s history.

Fortunately, the ESA’s Gaia spacecraft has been tracking over one billion stars in the Milky Way, giving Miller and his colleagues a massive compilation of data to search through. The team found three ultra-massive white dwarfs with kinematics indicating they could’ve left the Hyades cluster. The mass range for two of them made it unlikely that they did come from Hyades, but not for the third one. That object “appears to be a high-probability escapee” from the cluster, the authors write.

White dwarfs are as massive as the Sun but the size of the Earth. They’re made of electron degenerate matter and left their life of fusion long ago. The only energy they emit is remnant thermal energy.

White dwarfs are the end state of about 97% of the stars in the Milky Way. They’re governed by the Chandrasekhar Limit and can only have about 1.44 solar masses. If they gain more mass than that, typically by siphoning it from a binary companion, they explode as Type 1a supernovae, with the entire mass of the white dwarf dissipated into space.

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Artist view of a binary system before a type Ia supernova. Credit: Adam Makarenko/W. M. Keck Observatory

Hyades’ escaped white dwarf is called an ultra-massive white dwarf. These types of white dwarfs have 1.10 or more solar masses. That’s well below the Chandrasekhar limit but well above the average white dwarf mass of about 0.6 solar masses. They’re important outliers in the astrophysical study of white dwarfs. High-mass white dwarfs typically come from two progenitor stars in a binary pair, where one of the white dwarfs siphons material away from the other, increasing its mass.

But the Hyades ultra-massive white dwarf has a mass of 1.317 solar masses and an age consistent with only a single progenitor. It’s potentially the most massive white dwarf to come from a single progenitor and is also the most massive single progenitor star to be strongly associated with an open cluster.

“Assuming a single-stellar evolution formation channel, we estimate a 97.8% chance that the candidate is a true escapee from the Hyades,” the researchers write.

Why is this otherwise unassuming star significant? Because it typically requires two progenitor stars, with one siphoning mass from the other, to create a white dwarf this massive.

“This provides a critical observational benchmark for white dwarfs created from
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5 Reasons You Must Backpack the Teton Crest Trail

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By Michael Lanza

On my first backpacking trip on the Teton Crest Trail in Grand Teton National Park, camped on Death Canyon Shelf, a broad, boulder-strewn and wildflower-carpeted bench at 9,500 feet, I awoke to the sound of heavy clomping outside my tent. I unzipped the tent door to investigate—and saw a huge bull elk standing just outside my nylon walls.

As I’ve come to learn over more than 20 trips to the Tetons since that first one over three decades ago, that elk encounter symbolized just one of several compelling reasons why every backpacker should move the Teton Crest Trail to the top of their to-do list: the wildlife. Where it occurred illustrates another reason: After years of backpacking all over the United States—including the 10 years I spent as a field editor for Backpacker magazine and even longer running this blog—Death Canyon Shelf is still one of my all-time favorite backcountry campsites.

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Hi, I’m Michael Lanza, creator of The Big Outside, which has made several top outdoors blog lists. 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 to learn how I can help you plan your next trip.

Watching the sunset from a campsite in the North Fork Cascade Canyon, Grand Teton National Park.
” data-image-caption=”Watching the sunset from a campsite in the North Fork Cascade Canyon on the Teton Crest Trail in Grand Teton National Park.
” data-medium-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?fit=200%2C300&ssl=1″ data-large-file=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?fit=683%2C1024&ssl=1″ src=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?resize=432%2C648&ssl=1″ alt=”Watching the sunset from a campsite in the North Fork Cascade Canyon, Grand Teton National Park.” class=”wp-image-36411″ style=”width:432px;height:648px” width=”432″ height=”648″ srcset=”https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?w=800&ssl=1 800w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?resize=200%2C300&ssl=1 200w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?resize=768%2C1152&ssl=1 768w, https://i0.wp.com/thebigoutside.com/wp-content/uploads/2019/11/Tet19-090-A-campsite-on-the-Teton-Crest-Trail-North-Fork-Cascade-Canyon-Grand-Teton-N.P.jpg?resize=683%2C1024&ssl=1 683w” sizes=”(max-width: 432px) 100vw, 432px” data-recalc-dims=”1″ />Watching the sunset from a campsite in the North Fork Cascade Canyon, Grand Teton National Park.

And I certainly consider the Teton Crest Trail one of the 10 best backpacking trips in America. It’s the one I keep going back to again and again. (Read about my most recent trip.)

I think the five reasons I lay out below will give you insights into questions you might have about this classic hike—and inspire you to go do it.

But know this important planning detail: The

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How to Get a Permit to Backpack the Teton Crest Trail

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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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