THE SOCIETY FOR POPULAR ASTRONOMY
Electronic News Bulletin No. 598 2024 April 28
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DESI LOOKS 11 BILLION YEARS INTO THE PAST TO REVEAL MOST DETAILED VIEW EVER OF THE EXPANDING UNIVERSE
NOIRLab
The Dark Energy Spectroscopic Instrument is conducting a five-year survey to create the largest 3D map of the Universe ever. Astronomers are now performing initial analysis of the survey’s first-year data. Using spectra of nearby galaxies and distant quasars, astronomers report that they have measured the expansion history of the Universe with the highest precision ever, providing an unprecedented look at the nature of dark energy and its effect on the Universe's large-scale structure.
Since beginning its survey of the sky in 2021 the Dark Energy Spectroscopic Instrument (DESI) has observed a new set of 5000 galaxies every 20 minutes, totalling more than 100,000 galaxies per night, in its quest to create the largest 3D map of the Universe ever. Using the survey’s first-year data, which contains the largest extragalactic spectroscopic sample ever collected, astronomers report that they have measured the Universe’s expansion history over the last 11 billion years with a precision better than 1%. These measurements confirm the basics of our best model of the Universe, while also uncovering some tantalizing areas to explore with more data.
To map the cosmos, DESI collects light from millions of galaxies across more than a third of the entire sky. By breaking down the light from each galaxy into its spectrum of colors, DESI can determine how much the light has been redshifted, or stretched to a longer wavelength, by the expansion of the Universe during the billions of years it traveled before reaching Earth. In general, the higher the redshift the further away the galaxy is.
Equipped with 5000 tiny robotic ‘eyes,’ DESI is able to perform this measurement at an unprecedented rate. In its first year alone DESI surpassed all previous surveys of its kind in terms of quantity and quality. With incredible depth and precision, DESI has brought new insight to one of the biggest mysteries in physics: dark energy — the unknown ingredient causing the expansion of our Universe to accelerate.
“The DESI instrument has transformed the Mayall Telescope into the world’s premier cosmic cartography machine,” says Pat McCarthy, Director of NOIRLab. “The DESI team has set a new standard for studies of large-scale structure in the Universe. These first-year data are only the beginning of DESI’s quest to unravel the expansion history of the Universe and they hint at the extraordinary science to come."
DESI’s first-year data have allowed astronomers to measure the expansion rate of the Universe out to 11 billion years in the past, when the Universe was only a quarter of its current age, using a feature of the large-scale structure of the Universe called Baryon Acoustic Oscillations (BAO).
BAO are the leftover imprint of pressure waves that permeated the early Universe when it was nothing but a hot, dense soup of subatomic particles. As the Universe expanded and cooled the waves stagnated, freezing the ripples in place and seeding future galaxies in the dense areas. This pattern, resembling the rippling surface of a pond after a handful of pebbles is tossed in, can be seen in DESI’s detailed map, which shows strands of galaxiesclustered together, separated by voids where there are fewer objects.
At a certain distance, the BAO pattern becomes too faint to detect using typical galaxies. So instead astronomers look at the ‘shadow’ of the pattern as it’s backlit by extremely distant, bright galactic cores known as quasars. As the quasars’ light travels across the cosmos it gets absorbed by intergalactic clouds of gas, allowing astronomers to map the pockets of dense matter. To implement this technique, researchers used 450,000 quasars — the largest set ever collected for this type of study.
With DESI’s unique ability to map millions of objects both near and far, the BAO pattern can be used as a cosmic ruler. By mapping nearby galaxies and distant quasars, astronomers can measure the spread of the ripples across several periods of cosmic history to see how dark energy has stretched the scale over time. “We’re incredibly proud of the data, which have produced world-leading cosmology results,” said Michael Levi, DESI director and LBNL scientist. “So far we’re seeing basic agreement with our best model of the Universe, but we’re also seeing some potentially interesting differences that could indicate dark energy is evolving with time.”
While the expansion history of the Universe may be more complex than previously imagined, confirmation of this must await the completion of the DESI project. By the end of its five-year survey DESI plans to map over 3 million quasars and 37 million galaxies. As more data are released, astronomers will further improve their results.
“This project is addressing some of the biggest questions in astronomy, like the nature of the mysterious dark energy that drives the expansion of the Universe,” says Chris Davis, NSF program director for NOIRLab. “The exceptional and continuing results yielded by the NSF Mayall telescope with DOE DESI will undoubtedly drive cosmology research for many years to come.”
“We are delighted to see cosmology results from DESI's first year of operations," said Gina Rameika, associate director for High Energy Physics at the Department of Energy. "DESI continues to amaze us with its stellar performance and how it is shaping our understanding of dark energy in the Universe."
Data from DESI’s survey will work harmoniously with future sky surveys conducted by Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, with each instrument’s strength complementing the others. The DESI collaboration is currently investigating potential upgrades to the instrument and planning to expand their cosmological exploration into a second phase, DESI-II, as recommended in a recent report by the U.S. Particle Physics Project Prioritization Panel.
While the DESI year-one data are not yet publicly available, researchers can access the early data release as searchable databases of catalogs and spectra via the Astro Data Lab and SPARCL at the Community Science and Data Center, a Program of NSF NOIRLab.
EUROPE PREPARES FOR MARS COURIER
ESA
The first round-trip to the Red Planet will see a European orbiter bringing martian samples back to Earth. ESA is opening the door to industry to build the spacecraft that will deliver the precious rocks, dust and gas from Mars – the key to understanding whether life ever existed on our closest planetary neighbour.
This ‘take-away’ service is called the Earth Return Orbiter, and will be ESA’s major contribution to the Mars Sample Return campaign. The ESA Orbiter will carry NASA’s Capture and Containment and Return System, which will rely on the ESA-led spacecraft for transit to and from Mars.
Three launches from Earth and one from Mars – the first ever from another planet –, two rovers and an autonomous capture in Mars orbit are all part of an ambitious series of missions that ESA is embarking on together with NASA. The campaign aims to bring at least 500 grams of samples back from the Jezero crater that once held a lake and contains an ancient preserved river delta. The rocks in the area preserve information about Mars’ diverse geology.
NASA’s Mars 2020 rover that is slated for launch in July 2020 will scientifically select the best samples to store in tubes and deposit them onto the martian surface for later retrieval. ESA is also studying concepts for a small ‘fetch’ rover to scurry quickly across the martian surface to locate and recover the stored samples.
It would then carry them back to a football-sized canister that would be launched with a NASA Mars Ascent System – a small rocket. The Earth Return Orbiter will capture the canister in orbit and transfer it safely to Earth, a return trip that will take about 13 months.
It would then carry them back to a football-sized canister that would be launched with a NASA Mars Ascent System – a small rocket. The Earth Return Orbiter will capture the canister in orbit and transfer it safely to Earth, a return trip that will take about 13 months. “We will have the responsibility of finding, capturing and transporting these precious martian treasures home for careful analysis in state-of-the-art labs on our planet,” explains Sanjay Vijendran, ESA’s Mars Sample Return campaign coordinator. “It’s an interplanetary treasure hunt!”
Bringing Mars back to Earth
The Earth Return Orbiter is set to get onto the launch pad by 2026 from Europe’s spaceport in Kourou, French Guiana. Through this call, ESA will be selecting a prime contractor for the spacecraft. “The mission is becoming a reality, and we are proud to give European industry the chance to join the challenge,” says Orson Sutherland, study manager for the Earth Return Orbiter.
The main challenges are the electric propulsion and power generation. “Not to forget finding and navigating the spacecraft to rendezvous with the football sized orbiting sample over 50 million km away from ground control,” adds Orson. The spacecraft will use technological heritage from ESA’s most recently launched science mission, BepiColombo: both use electric propulsion and multi-stage detachable modules. “Europe is ready to do its bit for the Mars Sample Return campaign, in close partnership with NASA, and is up to the challenge of putting the spacecraft onto the launch pad in 2026,” says Orson.
GHOSTLY STELLAR TENDRILS CAPTURED IN LARGEST DECam IMAGE EVER RELEASED.
NOIRLab
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This colourful web of wispy gas filaments is the Vela Supernova Remnant, an expanding nebula of cosmic debris left over from a massive star that exploded about 11,000 years ago. This image was taken with the Department of Energy-fabricated Dark Energy Camera (DECam), mounted on the US National Science Foundation's Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab. The striking reds, yellows, and blues in this image were achieved through the use of three DECam filters that each collect a specific color of light. Separate images were taken in each filter and then stacked on top of each other to produce this high-resolution image that contains 1.3 gigapixels and showcases the intricate web-like filaments snaking throughout the expanding cloud of gas.
Credit:CTIO/NOIRLab/DOE/NSF/AURA
Image Processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani & D. de Martin (NSF’s NOIRLab)
With the powerful, 570-megapixel Department of Energy-fabricated Dark Energy Camera (DECam), astronomers have constructed a massive 1.3-gigapixel image showcasing the central part of the Vela Supernova Remnant, the cosmic corpse of a gigantic star that exploded as a supernova. DECam is one of the highest-performing wide-field imaging instruments in the world and is mounted on the US National Science Foundation's Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory, a Program of NSF’s NOIRLab.
This colourful web of wispy gas filaments is the Vela Supernova Remnant, an expanding nebula of cosmic debris left over from a massive star that exploded about 11,000 years ago. Located around 800 light-years away in the constellation Vela (the Sails), this nebula is one of the nearest supernova remnants to Earth. Though the unnamed star ended its life thousands of years ago, the shockwave its death produced is still propagating into the interstellar medium, carrying glowing tendrils of gas with it.
This image is one of the biggest ever made of this object and was taken with the state-of-the-art wide-field Dark Energy Camera (DECam), built by the Department of Energy and mounted on the US National Science Foundation's Víctor M. Blanco 4-meter Telescope at Cerro Tololo Inter-American Observatory in Chile, a Program of NSF’s NOIRLab. The striking reds, yellows, and blues in this image were achieved through the use of three DECam filters that each collect a specific color of light. Separate images were taken in each filter and then stacked on top of each other to produce this high-resolution color image that showcases the intricate web-like filaments snaking throughout the expanding cloud of gas. This is also the largest DECam image ever released publicly, containing an astounding 1.3 gigapixels [1].
The Vela Supernova Remnant is merely the ghost of a massive star that once was. When the star exploded 11,000 years ago, its outer layers were violently stripped away and flung into the surrounding region, driving the shockwave that is still visible today. As the shockwave expands into the surrounding region, the hot, energized gas flies away from the point of detonation, compressing and interacting with the interstellar medium to produce the stringy blue and yellow filaments seen in the image. The Vela Supernova Remnant is a gigantic structure, spanning almost 100 light-years and extending to twenty times the diameter of the full Moon in the night sky.
Despite the dramatics of the star’s final moments, it wasn’t entirely wiped from existence. After shedding its outer layers, the core of the star collapsed into a neutron star — an ultra-dense ball consisting of protons and electrons that have been smashed together to form neutrons. The neutron star, named the Vela Pulsar, is now an ultra-condensed object with the mass of a star like the Sun contained in a sphere just a few kilometers across. Located in the lower left region of this image, the Vela Pulsar is a relatively dim star that is indistinguishable from its thousands of celestial neighbors. Still reeling from its explosive death, the Vela Pulsar spins rapidly on its own axis and possesses a powerful magnetic field. These properties result in twin beams of radiation that sweep the sky 11 times per second, just like the consistent blips of a rotating lighthouse bulb.
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This high-quality image demonstrates the incredible deep and wide capabilities of DECam. From its vantage point in the Chilean Andes, the Blanco telescope receives light that has traveled across the Universe. After entering the telescope’s tube, the light is reflected by a mirror 4-meters (13-feet) wide — a massive, aluminum-coated and precisely shaped piece of glass roughly the weight of a semi-truck. The light is then guided into the optical innards of DECam, passing through a corrective lens nearly a meter (3.3 feet) across before falling on a grid of 62 charge-coupled devices (CCDs), which act like the ‘eyes’ of the camera. The incoming light is then converted into electrical signals which are read out as pixels.
A single image taken with DECam has 570 megapixels, so with multiple exposures stacked on top of one another, the amount of detail that can be captured is truly remarkable. Owing to DECam’s large mosaic of CCDs, astronomers are able to create mesmerizing images of faint astronomical objects, such as the Vela Supernova Remnant, that offer a limitless starscape to explore.
NASA'S WEBB PROBES AN EXTREME STARBURST GALAXY.
NASA
A team of astronomers has used NASA’s James Webb Space Telescope to survey the starburst galaxy Messier 82 (M82). Located 12 million light-years away in the constellation Ursa Major, this galaxy is relatively compact in size but hosts a frenzy of star formation activity. For comparison, M82 is sprouting new stars 10 times faster than the Milky Way galaxy.
Led by Alberto Bolatto at the University of Maryland, College Park, the team directed Webb’s NIRCam (Near-Infrared Camera) instrument toward the starburst galaxy’s center, attaining a closer look at the physical conditions that foster the formation of new stars.
“M82 has garnered a variety of observations over the years because it can be considered as the prototypical starburst galaxy,” said Bolatto, lead author of the study. “Both NASA’s Spitzer and Hubble space telescopes have observed this target. With Webb’s size and resolution, we can look at this star-forming galaxy and see all of this beautiful, new detail.”
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On the left is the starburst galaxy M82 as observed by NASA’s Hubble Space Telescope in 2006. The small box at the galaxy’s core corresponds to the area captured so far by the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope. The red filaments as seen by Webb are the polycyclic aromatic hydrocarbon emission, which traces the shape of the galactic wind. In the Hubble image, light at .814 microns is colored red, .658 microns is red-orange, .555 microns is green, and .435 microns is blue (filters F814W, F658N, F555W, and F435W, respectively). In the Webb image, light at 3.35 microns is colored red, 2.50 microns is green, and 1.64 microns is blue (filters F335M, F250M, and F164N, respectively).
CREDIT: NASA, ESA, CSA, STScI, A. Bolatto (University of Maryland)
A Vibrant Community of Stars
Star formation continues to maintain a sense of mystery because it is shrouded by curtains of dust and gas, creating an obstacle in observing this process. Fortunately, Webb’s ability to peer in the infrared is an asset in navigating these murky conditions. Additionally, these NIRCam images of the very center of the starburst were obtained using an instrument mode that prevented the very bright source from overwhelming the detector.
While dark brown tendrils of heavy dust are threaded throughout M82’s glowing white core even in this infrared view, Webb’s NIRCam has revealed a level of detail that has historically been obscured. Looking closer toward the center, small specks depicted in green denote concentrated areas of iron, most of which are supernova remnants. Small patches that appear red signify regions where molecular hydrogen is being lit up by a nearby young star’s radiation.
“This image shows the power of Webb,” said Rebecca Levy, second author of the study at the University of Arizona, Tucson. “Every single white dot in this image is either a star or a star cluster. We can start to distinguish all of these tiny point sources, which enables us to acquire an accurate count of all the star clusters in this galaxy.”
Finding Structure in Lively Conditions
Looking at M82 in slightly longer infrared wavelengths, clumpy tendrils represented in red can be seen extending above and below the galaxy’s plane. These gaseous streamers are a galactic wind rushing out from the core of the starburst. One area of focus for this research team was understanding how this galactic wind, which is caused by the rapid rate of star formation and subsequent supernovae, is being launched and influencing its surrounding environment. By resolving a central section of M82, scientists could examine where the wind originates, and gain insight on how hot and cold components interact within the wind.
Webb’s NIRCam instrument was well-suited to trace the structure of the galactic wind via emission from sooty chemical molecules known as polycyclic aromatic hydrocarbons (PAHs). PAHs can be considered as very small dust grains that survive in cooler temperatures but are destroyed in hot conditions.
Much to the team’s surprise, Webb’s view of the PAH emission highlights the galactic wind’s fine structure – an aspect previously unknown. Depicted as red filaments, the emission extends away from the central region where the heart of star formation is located. Another unanticipated find was the similar structure between the PAH emission and that of hot, ionized gas. “It was unexpected to see the PAH emission resemble ionized gas,” said Bolatto. “PAHs are not supposed to live very long when exposed to such a strong radiation field, so perhaps they are being replenished all the time. It challenges our theories and shows us that further investigation is required.”
Lighting a Path Forward
In the near future, the team will have spectroscopic observations of M82 from Webb ready for their analysis, as well as complementary large-scale images of the galaxy and wind. Spectral data will help astronomers determine accurate ages for the star clusters and provide a sense of timing for how long each phase of star formation lasts in a starburst galaxy environment. On a broader scale, inspecting the activity in galaxies like M82 can deepen astronomers’ understanding of the early universe.
“Webb’s observation of M82, a target closer to us, is a reminder that the telescope excels at studying galaxies at all distances,” said Bolatto. “In addition to looking at young, high-redshift galaxies, we can look at targets closer to home to gather insight into the processes that are happening here – events that also occurred in the early universe.”
These findings have been accepted for publication in The Astrophysical Journal.The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.
Bulletin compiled by Eleni Tsiakaliari
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