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Brown dwarfs are strange things. They are in the middle ground between planets and stars. A star is defined as an object massive enough for helium to fuse into hydrogen into its core, while a planet is too small for core fusion to occur. It seems a simple distinction until you learn about fusion. Anything with a mass below about 13 Jupiters is too small for fusion to occur, and is thus a planet. If your mass is about about 80 Jupiters, then you can fuse helium and are therefore a star. But if your mass is between 13 and 80 Jupiters, things get interesting. You can’t fuse hydrogen to shine brightly, but you can fuse lithium into other elements. This is known as lithium burning. It doesn’t provide lots of energy, but it is technically nuclear fusion.

Because of this effect, brown dwarfs can be difficult to identify. Large and young brown dwarfs can be as hot and bright as a small star, while older or smaller brown dwarfs look like large planets. This is because, unlike stars, brown dwarfs cool down over time. They are often brightest at infrared wavelengths, and so they are often identified by their infrared spectrum.

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The distribution of stars near Earth. Credit: NASA, ESA, and A. Feild (STScI)

But one odd aspect about brown dwarfs is that they seem to be rarer than they should be. When you count the number of stars in the local universe, yellow stars such as our Sun are more common than giant stars, and red dwarf stars are much more common than yellow ones. You would expect then that brown dwarfs are more common than red dwarfs. But so far we’ve found fewer brown dwarfs than even yellow stars. Part of that is due to the fact that brown dwarfs are cool and dim, but even when we take that into consideration we should see more of them. It’s known as the brown dwarf desert problem.

But an accidental discovery might be the solution to this mystery. It was discovered by NASA’s Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE), and named “The Accident.” It is a brown dwarf that didn’t show up in sky surveys looking for brown dwarfs because it doesn’t look like a brown dwarf. Brown dwarfs can be identified by their infrared spectra, but each spectrum depends on the composition of the brown dwarf as well as its temperature. The spectrum of The Accident is odd because it’s dim where you’d expect it to be bright, and bright where it’s typically dim.

The moving spot is a brown dwarf known as The Accident. Credit: NASA/JPL-Caltech/Dan Caselden

The spectrum of The Accident suggests that it contains very little methane, and that could mean that it’s extremely old. Methane is a molecule of carbon and hydrogen, and although hydrogen has been around since the cosmic beginning, carbon only appeared after the first generation of stars had died. Thus, the spectrum suggests that this brown dwarf formed during that first generation period. We’ve known that early generation brown dwarfs likely exist, but we figured they are rare. But The Accident is only 50 light-years away from us, so either it was an extraordinarily lucky find or this type of brown dwarf is fairly common. This could explain the brown dwarf desert. Countless brown dwarfs are out there, but they have unusual spectra so we’ve overlooked them.

The discovery of a single brown dwarf isn’t enough to settle the matter. But now that we know what old brown dwarfs can look like, we can look for more. And this time what we find will be no accident.

Reference: Kirkpatrick, J. Davy, et al. “The Enigmatic Brown Dwarf WISEA J153429. 75-104303.3 (aka “The Accident”).” The Astrophysical Journal Letters 915.1 (2021): L6.

The post Brown Dwarfs are Probably Much More Common in the Milky Way Than Previously Believed appeared first on Universe Today.

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Communicating With a Relativistic Spacecraft Gets Pretty Weird

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Someday, in the not-too-distant future, humans may send robotic probes to explore nearby star systems. These robot explorers will likely take the form of lightsails and wafercraft (a la Breakthrough Starshot) that will rely on directed energy (lasers) to accelerate to relativistic speeds – aka. a fraction of the speed of light. With that kind of velocity, lightsails and wafercraft could make the journey across interstellar space in a matter of decades instead of centuries (or longer!) Given time, these missions could serve as pathfinders for more ambitious exploration programs involving astronauts.

Of course, any talk of interstellar travel must consider the massive technical challenges this entails. In a recent paper, a team of engineers and astrophysicists considered the effects that relativistic space travel will have on communications. Their results showed that during the cruise phase of the mission (where a spacecraft is traveling close to the speed of light), communications become problematic for one-way and two-way transmissions. This will pose significant challenges for crewed missions but will leave robotic missions largely unaffected.

The team consisted of David Messerschmitt, a Professor Emeritus of Electrical Engineering and Computer Science at the University of California at Berkeley; Ian Morrison, a Research Fellow at Curtin University’s International Centre for Radio Astronomy Research (ICRAR) and the communications and signal processing developer Astro Signal Pty Ltd; Thomas Mozdzen, a research scientist in the School of Earth and Space Exploration at Arizona State University; and Philip Lubin, a professor of physics and the head of the Experimental Cosmology Group at UC Santa Barbara. The preprint of their paper recently appeared online and is being reviewed for publication by Elsevier.

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An artist’s illustration of a lightsail powered by a radio beam (red) generated on the surface of a planet. Credit: M. Weiss/CfA

For their study, the team considered both robotic (uncrewed) and crewed mission profiles. The former consists of concepts similar to the Starshot and Directed Energy Propulsion for Interstellar Exploration (DEEP-In) – aka. Starlight – concepts. This latter concept is one that Prof. Lubin and his colleagues at UCSB Experimental Cosmology Group have been developing since 2014 through the NASA Innovative Advanced Concepts (NIAC) program. However, their analysis differed since it considers scenarios where spacecraft are approaching the speed of light – rather than the 10% to 20% called for with the Starlight and Starshot concepts.

For uncrewed missions, remote control operations and data transmission require reliable communications during certain phases. For crewed missions, however, maintaining persistent communications with home is crucial to the long-term well-being of astronauts. Regardless of the mission profile, communications invariably come down to transmissions in the electromagnetic spectrum (radio waves, lasers, etc.) and how they propagate through space. As the team told Universe Today via email:

“The assumption we’re making is that communication signals are electromagnetic, hence conveyed via photons. This relates to the propagation speed of a communication signal, which relates to the propagation delay. The timing/latency relationships are independent of the wavelength and hence apply equally to radio, microwave, or optical.”

Another key consideration is that communications at relativistic speeds must take into account the effects of Special Relativity. In short, a spacecraft traveling at a significant fraction of the speed of light will experience time dilation, where its internal clocks will advance more slowly than mission clocks on Earth. Another consideration is that communications to and from the mission will be subject to Doppler Shift. As Special Relativity teaches us, the speed of light is constant in a vacuum and does not speed up or slow down based on the motion of the observer or source.

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Review: Himali Limitless Grid Fleece Hoodie

Hooded Fleece Jacket
Himali Limitless Grid Fleece Hoodie
$160, 9.2 oz./261g (men’s medium)
Sizes: men’s S-XXL

The evolution of fleece has traced an arc toward efficiency and versatility that now seems to be reaching its apex in lightweight fleece hoodies, perfectly exemplified by Himali’s Limitless Grid Fleece Hoodie. The breadth of activities, conditions, and environments where I’ve worn it just this fall speak to my point, from a 13-hour, four-summit dayhike in Utah’s Wasatch Range to a short hike in southern New Hampshire, backpacking in southern Utah’s Escalante region, camping and climbing in Idaho, and a local trail run in the chilly, fading daylight of a November afternoon.

Here’s the first conclusion I drew about this fleece hoodie: It’s basically a warm, midweight jersey with a full front zipper and a hood. It replaced—and provided more versatility than—a midweight, long-sleeve top when I wore it over a synthetic T-shirt in the falling temperatures of an October evening hiking by headlamp in the dark for the last two hours of an 18-mile, 7,300-foot, partly off-trail dayhike in the Wasatch Range—when I needed warmth (and got a big boost from the hood) plus the ability to speedily dry my sweaty T-shirt.

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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.

The Himali Limitless Grid Fleece Hoodie.
” data-image-caption=”The Himali Limitless Grid Fleece Hoodie.
” data-medium-file=”″ data-large-file=”″ src=”″ alt=”The Himali Limitless Grid Fleece Hoodie.” class=”wp-image-61126″ srcset=” 1024w, 300w, 768w, 150w, 1200w” sizes=”(max-width: 900px) 100vw, 900px” data-recalc-dims=”1″ />The Himali Limitless Grid Fleece Hoodie.

It served the same purpose in my layering system for three days in early October backpacking the 22-mile Boulder Mail Trail-Death Hollow-Escalante River Loop in the Grand Staircase-Escalante National Monument, shining especially in camp and for the first couple of hours hiking in shallow water down the shaded and cool canyon of Death Hollow on our second morning. Ditto on cool mornings and evenings in camp over a late-September weekend of climbing at Idaho’s City of Rocks National Reserve, pulling a down jacket over this hoodie in colder temps; and when I wore it as a middle layer under a rain shell on a 2.5-hour dayhike up a couple of wooded peaks along the Wapack Trail in southern New Hampshire on a rainy day with temps in the 40s Fahrenheit.

Lastly, it proved ideal worn over a lightweight, long-sleeve base layer on an hour-long trail run on a sunny day in mid-November,

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This Planet is Way Too Big for its Star

Scientists love outliers. Outliers are nature’s way of telling us what its boundaries are and where its limits lie. Rather than being upset when an outlier disrupts their understanding, scientists feed on the curiosity that outliers inspire.

It’s true in the case of a new discovery of a massive planet orbiting a small star. That goes against our understanding of how planets form, meaning our planet-formation model needs an update.

In a paper published in Science, researchers announced the discovery of a Neptune-mass exoplanet orbiting a low-mass star. The star is LHS 3154, an M-dwarf, or red dwarf star. It’s only 0.11 times as massive as the Sun, which is a normal mass for a red dwarf.

But what’s surprising is the size of the planet orbiting the star. The planet is called LHS 3154b, and it’s a monster compared to most planets orbiting red dwarfs. It has at least 13.2 Earth masses. That places it in the same range as Neptune, which has 17 Earth masses. LHS 3154b is also in a very close orbit, taking only 3.7 days to orbit the star.

“This discovery really drives home the point of just how little we know about the universe.”

Suvrath Mahadevan, Penn State University

The new paper is “A Neptune-mass exoplanet in close orbit around a very low-mass star challenges formation models.” The lead author is Gudmundur Stefansson, NASA Sagan Fellow in Astrophysics at Princeton University. Stefansson was a graduate student at Penn State while working on this discovery.

“This discovery really drives home the point of just how little we know about the universe,” said Suvrath Mahadevan, a Professor of Astronomy and Astrophysics at Penn State and co-author of the paper. “We wouldn’t expect a planet this heavy around such a low-mass star to exist.”

Why is this discovery surprising? It’s all about stars and their protoplanetary disks.

When a star forms, it starts as a protostar in the center of a solar nebula. As the star forms, a rotating disk of gas and dust called a protoplanetary disk forms around the star. Dense knots form in the disk, and this is how planets and planetesimals form. It’s a detailed process and one we don’t entirely understand. But what scientists do know, or thought they knew, is that the more mass there is in the disk, the more massive the planets that can form. And the mass in the disk scales steeply with the mass of the star.

It looks like this: massive star = massive disk = massive planets. Naturally, we consider the obverse to be true, too. Small star = small disk = small planets. But LHS 3154b and its star don’t conform to this. There simply shouldn’t have been enough mass in the protoplanetary disk for the planet to form.

“The planet-forming disk around the low-mass star LHS 3154 is not expected to have enough solid mass to make this planet,” Mahadevan said. “But it’s out there, so now we need to reexamine our understanding of how planets and stars form.”

It took a special instrument to spot the massive planet, and Mahadevan led the team of scientists that built it. It’s called the Habitable Zone Planet Finder or HPF, a spectrograph built at Penn State. HPF is designed to detect planets orbiting cool stars that might have liquid surface water. Small planets can be very difficult to detect around large, bright stars like our Sun because the Sun’s light overpowers everything else.

But around smaller cooler stars, planets close enough to have liquid water are much easier to find.

“Think about it like the star is a campfire. The more the fire cools down, the closer you’ll need to get to that fire to stay warm,” Mahadevan said. “The same is true for planets. If the star is colder, then a planet will need to be closer to that star if it is going to be warm enough to contain liquid water. If a planet has a close enough orbit to its ultracool star, we can detect it by seeing a very subtle change in the colour of the star’s spectra or light as it is tugged on by an orbiting planet.”

This artist's illustration helps explain how small planets are easier to detect around stars that are smaller and cooler than the Sun. Image Credit: Penn State / Penn State. Creative CommonsDid you miss our previous article…

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