It’s difficult to determine the shape of our galaxy. So difficult that only in the last century did we learn that the Milky Way is just one galaxy among billions. So it’s not surprising that despite all our modern telescopes and spacecraft we are still mapping the shape of our galaxy. And one of the more interesting discoveries is that the Milky Way is warped. One explanation for this is that our galaxy has undergone collisions, but a new study argues that it’s caused by dark matter.
The first evidence that the Milky Way isn’t a purely flat disk came from the Gaia Spacecraft. it has mapped the positions and motions of more than a billion stars, and from this we have some idea of our galaxies outer structure. For one thing, the Milky Way seems to extend outward more than we’ve thought, and the edge seems to have a rippled structure to it. Further analysis also shows a warp to the outer edge of the galactic disk. The general consensus is that these are caused by ancient galactic collisions, such as the collision with the Sagittarius dwarf galaxy about 6 billion years ago. This new study argues instead that warped galaxies such as ours are caused by a tilted halo of dark matter.
The galaxy ESO 510-G13 has a clearly warped shape. Credit: NASA and The Hubble Heritage Team (STScI/AURA)
We know that most galaxies, including our own, are surrounded by a massive halo of dark matter. Most of the mass in a galaxy is contained within this halo, so halos can affect the structure of galaxies over time. If the halo is tilted relative to the plane of a galaxy, the gravitational effects of the halo could skew the galactic disk. The question is whether this is significant or common enough to cause the structure we see in the Milky Way.
The authors begin by looking at data from the TNG50 run of the IllustrisTNG simulations. These are supercomputer simulations of galactic evolution that include cosmological evolution and dark matter as well as detailed magnetohydrodynamic interactions. From this data, the authors show that the inner region of the dark matter halo can be significantly tilted relative to the galactic plane and that these can be caused both by galactic collisions and near misses between galaxies. The orientation of the halos can persist for billions of years, which is plenty long enough to induce a galactic warp.
The simulated evolution of a warped galaxy. Credit: Han, et al
The team then looked at an archetypal galaxy within the TNG50 simulation, having a similar size and age to the Milky Way, including a titled dark matter halo. Based on 6 billion years of simulated evolution, the final result showed noted similarities between the observed Milky Way and the model galaxy.
Astronomers have observed other galaxies with a warped plane, and there is some evidence that as many as half of spiral galaxies in the Universe are warped to some degree. This suggests the influence of long-term and common gravitational interactions between a galaxy and its twisted halo. Of course, this is just one study, so further observations and simulations will be needed to understand the details of how many galaxies such as the Milky Way evolve.
Reference: Han, Jiwon Jesse, et al. “Tilted Dark Halos are Common, Long-Lived, and can Warp Galactic Disks.” arXiv preprint arXiv:2309.07208 (2023).
Reference: Poggio, Eloisa, et al. “Evidence of a dynamically evolving Galactic warp
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Titan Probably Doesn’t Have the Amino Acids Needed for Life to Emerge
Does Saturn’s largest moon, Titan, possess the necessary ingredients for life to exist? This is what a recent study published in Astrobiology hopes to address as a team of international researchers led by Western University investigated if Titan, with its lakes of liquid methane and ethane, could possess the necessary organic materials, such as amino acids, that could be used to produce life on the small moon. This study holds the potential to help researchers and the public better understand the geochemical and biological processes necessary for life to emerge throughout the cosmos.
Along with its liquid lakes of methane and ethane, Titan is also strongly hypothesized to possess a subsurface liquid water ocean like Saturn’s icy moon, Enceladus, and Jupiter’s icy moon, Europa. For the study, the researchers used data from impact cratering from comets to estimate the number of organic molecules that could relocate from Titan’s surface to its subsurface liquid water ocean. The team hypothesized that when comets strike Titan’s surface, their icy materials would melt from the heat of the impact and mix with the surface organics, resulting in a unique mixture. However, the heavier liquid water would then sink to the subsurface, slowly filling the subsurface ocean over time.
Artist’s cutaway illustration displaying Titan’s subsurface ocean (blue). (Credit: NASA/JPL)
After accounting for a presumed annual number of cometary impacts on Titan’s surface throughout its billions of years of existence, the researchers then calculated how much water would make its way from the surface to the subsurface ocean. In the end, the team concluded that the amount of glycine, which is the most basic amino acid that forms the proteins to create life, was measured at no greater than 7,500 kilograms/year (16,530 pounds/year). This amount approximately equals the size of a smaller African forest elephant, hence indicating number of organic materials that exist on Titan is quite miniscule.
“One elephant per year of glycine into an ocean 12 times the volume of Earth’s oceans is not sufficient to sustain life,” said Dr. Catherine Neish, who is an associate professor in the Department of Earth Sciences at Western University and lead author of the study. “In the past, people often assumed that water equals life, but they neglected the fact that life needs other elements, in particular carbon.”
While Dr. Neish’s study presents somewhat dire implications for finding life on Titan, this study comes on the heels of a recent investigation into how organic hazes on ancient Earth could have contained the necessary building blocks of life, including nucleobases and amino acids, which could hold implications for finding life on Titan due to the moon’s hazy atmosphere. For this study, the researchers used laboratory experiments to determine that “warm little ponds” on ancient Earth could host nucleobases. Both studies offer profound insights into the processes responsible for both creating and sustaining life beyond Earth, and further research is undoubtedly required to better understand these processes.
One such research opportunity that could help solidify these studies could be NASA’s upcoming Dragonfly mission, which is a quadcopter designed to search Titan’s surface for signs of potential habitability with Dr. Neish assigned as a mission co-investigator. Dragonfly currently has a scheduled launch date of July 2028, arriving at Saturn’s largest moon sometime in 2034. While Dragonfly will not be the first aircraft on another world, as that honor goes to NASA’s Ingenuity Mars Helicopter, it will be the first aircraft to land and operate in the outer solar system. Dragonfly will launch more than 20 years after the European Space Agency’s Huygens probe landed on Titan in January 2005, beaming back images of rounded rocks that could have formed from liquid processes.
What new discoveries will scientists make about Titan and its potential for life in the coming years and decades? Only time will tell, and this is why we science!
As always, keep doing science & keep looking up!
The post Titan Probably Doesn’t Have the Amino Acids Needed for Life to Emerge appeared first on Universe Today
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Astronomers Discover a New Meteor Shower. The Source is Comet 46P/Wirtanen
Like many of you, I love a good meteor shower. I have fond memories of the Leonid meteor storm back in 1999 when several hundred per hour were seen at peak. Sadly meteor storms are not that common unlike meteor showers of which, there are about 20 major showers per year. Wait, there’s another one and this time it comes from the debris left behind from Comet 46P/Wirtanen with an expected peak on December 12. Last year, 23 meteors were seen on that night that matched the location of the comets trail.
Comets (and some asteroids) leave a trail of debris behind them like a trail of celestial breadcrumbs. If the orbit of a comet crosses the orbit of the Earth then the particles from the debris (that are often no larger than grains of sand) collide with our atmosphere. At the immense speeds (of the order of 60 km per second, the particles falling through the atmosphere cause the gas to glow giving rise to the classic shooting star we see in the sky. Because the orbits of Earth and comets are relatively fixed, this process repeats itself every time we go through the same part of the orbit giving us the familiar annual meteor showers.
One such comet that it seems may become host to a new annual shower is Comet 46P/Wirtanen (46P). It nearly hit the headlines previously when it had been initially selected as the target for the Rosetta mission which, as you may recall, visited 67P/Churyumov-Gerasimenko instead. 46P is known as a short period comet taking 5.4 years to complete one orbit of the Sun. It is among the family of comets known as a Jupiter comet which has a most distant point from the Sun of between 5 and 6 astronomical units (1 AU is the average distance between the Sun and Earth). Observations have suggested it has a diameter of about 1.4km.
Comet 67P/Churyumov-Gerasimenko from Rosetta mission (Credit – NASA)
Due to the high levels of ice present in comets, it’s not unusual for active areas on their surface to appear as the ices sublimate into gasses or pockets of gas escape. Observations using the TRAPPIST telescope (The Transiting Planets and Planetesimals Small Telescope) suggest 40% of the surface is active which is higher than the usual 5-10% for Jupiter family comets. A recent study found the presence of mm sized dust particles in the comet’s coma which should be visible upon entering Earth’s atmosphere.
The orbit of 46P has a very low minimum orbit intersection distance (MOID) to Earth of just 0.071AU. The MOID between two objects that orbit a common point is the distance between the closest points of their orbits. The low MOID and the mm sized particles mean there is a high liklihood it could be the source of a meteor shower. Previous observations however have revealed no positive confirmation of peaks in 2017 and 2019.
During the 2017 and 2019 predictions, it seems the low velocity of the particles coupled with the radiant (the point of apparent origin of the shower) below the horizon suggest that visibility may have been severely limited. The radiant of this predicted shower is in the constellation Sculptor and the shower has been dubbed the Lambda Sculptorids.
The prediction for the 2023 shower, which predicted an encounter from a stream of debris from an outburst in 1974, suggested an outburst of meteors on December 12 between 12:08 and 20:06. A further outburst was predicted between 17:05 and 06:26 on December 13. The team who presented their findings in Astronomy and Astrophysics reported meteor activity as predicted and detected 23 meteors from the new shower on the night of December 12 2023. The team are now looking at the models to see what we might expect to see this year and whether Lamba Sculptorids need to be added to our list of annual meteor showers.
Source : Observations of the new meteor shower from comet 46P/Wirtanen
The post Astronomers Discover a New Meteor Shower. The Source is Comet 46P/Wirtanen appeared first on Universe Today.
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The 12 Best Dayhikes in Yosemite
By Michael Lanza
The natural beauty, variety, pristine quality, and scale of America’s National Park System have no parallel in the world. Still, a handful of flagship parks rise above the rest—including, unquestionably, Yosemite. Created in 1890, our third national park harbors some of the most breathtaking and inspiring wild lands in the entire parks system. And you can reach much of Yosemite’s finest scenery on dayhikes.
This story shares my picks for the 12 best dayhikes in Yosemite, from popular hikes like Half Dome, the Mist Trail, and Upper Yosemite Falls to some trails and peaks you may not have heard of—including the nearly 11,000-foot summit known to have “the best 360 in Yosemite.”
This list of Yosemite’s best hikes is drawn from my numerous trips dayhiking and backpacking all over the park going back more than 30 years, including the 10 years I spent as a field editor for Backpacker magazine and even longer running this blog. Use this story as your guide and you will see the best scenery in Yosemite that’s accessible on a moderate to full day of hiking.
Please share your thoughts on any of these hikes or your own favorites in Yosemite in the comments section at the bottom of this story. I try to respond to all comments.
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-books to classic backpacking trips. Click here to learn how I can help you plan your next trip.
May Lake in Yosemite National Park.
” data-image-caption=”May Lake in Yosemite National Park.
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May Lake and Mount Hoffmann
2.4 to 6 miles, 500 to 2,100 feet up and down
From the 10,850-foot summit of Mount Hoffmann (lead photo at top of story) in the geographic center of Yosemite—often described as having “the best 360 in Yosemite”—you’ll look out over virtually the entire park, seeing Half Dome, Clouds Rest, and Yosemite Valley, the Clark and Cathedral Ranges, and the sea of peaks sprawling across northern Yosemite. The hike culminates with a steep, third-class scramble up the final 200 feet to the summit, where you stand at the brink of cliffs with serious exposure (although you don’t have to stand at that dizzying edge).
The summit of Yosemite’s Mount Hoffmann.
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