SPACE
Researchers identify two of the Milky Way's earliest building blocks
MAX PLANCK INSTITUTE FOR ASTRONOMY
IMAGE:
A VISUALIZATION OF THE MILKY WAY GALAXY, WITH THE STARS THAT KHYATI MALHAN AND HANS-WALTER RIX IDENTIFIED IN THE GAIA DR3 DATA SET AS BELONGING TO SHIVA AND SHAKTI SHOWN AS COLORED DOTS. SHIVA STARS ARE SHOWN IN GREEN AND SHAKTI STARS IN PINK. THE COMPLETE ABSENCE OF GREEN AND PINK MARKERS IN SOME REGIONS DOES NOT MEAN THAT THERE ARE NO STARS FROM SHIVA OR SHAKTI THERE, AS THE DATA SET USED FOR THIS STUDY ONLY COVERS SPECIFIC REGIONS WITHIN OUR GALAXY.
view moreCREDIT: S. PAYNE-WARDENAAR / K. MALHAN / MPIA
The early history of our home galaxy, the Milky Way, is one of joining smaller galaxies, which makes for fairly large building blocks. Now, Khyati Malhan and Hans-Walter Rix of the Max Planck Institute for Astronomy have succeeded in identifying what could be two of the earliest building blocks that can still be recognized as such today: proto-galactic fragments that merged with an early version of our Milky Way between 12 and 13 billion years ago, at the very beginning of the era of galaxy formation in the Universe. The components, which the astronomers have named Shakti and Shiva, were identified by combining data from ESA’s astrometry satellite Gaia with data from the SDSS survey. For astronomers, the result is the equivalent of finding traces of an initial settlement that grew into a large present-day city.
Tracing the origins of stars that came from other galaxies
When galaxies collide and merge, several processes happen in parallel. Each galaxy carries along its own reservoir of hydrogen gas. Upon collision, those hydrogen gas clouds are destabilized, and numerous new stars are formed inside. Of course, the incoming galaxies also already have their own stars, and in a merger, stars from the galaxies will mingle. In the long run, such “accreted stars” will also account for some of the stellar population of the newly-formed combined galaxy. Once the merger is completed, it might seem hopeless to identify which stars came from which predecessor galaxy. But in fact, at least some ways of tracing back stellar ancestry exist.
Help comes from basic physics. When galaxies collide and their stellar populations mingle, most of the stars retain very basic properties, which are directly linked to the speed and direction of the galaxy in which they originated. Stars from the same pre-merger galaxy share similar values for both their energy and what physicists call angular momentum – the momentum associated with orbital motion or rotation. For stars moving in a galaxy’s gravitational field, both energy and angular momentum are conserved: they remain the same over time. Look for large groups of stars with similar, unusual values for energy and angular momentum – and chances are, you might find a merger remnant.
Additional pointers can assist identification. Stars that formed more recently contain more heavier elements, what astronomers call “metals”, than stars that formed a long time ago. The lower the metal content (“metallicity”), the earlier the star presumably formed. When trying to identify stars that already existed 13 billion years ago, one should look for stars with very low metal content (“metal-poor”).
Virtual excavations in a large data set
Identifying the stars that joined our Milky Way as parts of another galaxy has only become possible comparatively recently. It requires large, high-quality data sets, and the analysis involves sifting the data in clever ways so as to identify the searched-for class of objects. This kind of data set has only been available for a few years. The ESA astrometry satellite Gaia provides an ideal data set for this kind of big-data galactic archeology. Launched in 2013, it has produced an increasingly accurate data set over the past decade, which by now includes positions, changes in position and distances for almost 1.5 billion stars within our galaxy.
Gaia data revolutionized studies of the dynamics of stars in our home galaxy, and has already led to the discovery of previously unknown substructures. This includes the so-called Gaia Enceladus/Sausage stream, a remnant of the most recent larger merger our home galaxy has undergone, between 8 and 11 billion years ago. It also includes two structures identified in 2022: the Pontus stream identified by Malhan and colleagues and the “poor old heart” of the Milky Way identified by Rix and colleagues. The latter is a population of stars that newly formed during the initial mergers that created the proto-Milky Way, and continue to reside in our galaxy’s central region.
Traces of Shakti and Shiva
For their present search, Malhan and Rix used Gaia data combined with detailed stellar spectra from the Sloan Digital Sky Survey (DR17). The latter provide detailed information about the stars’ chemical composition. Malhan says: “We observed that, for a certain range of metal-poor stars, stars were crowded around two specific combinations of energy and angular momentum.”
In contrast with the “poor old heart”, which was also visible in those plots, the two groups of like-minded stars had comparatively large angular momentum, consistent with groups of stars that had been part of separate galaxies which had merged with the Milky Way. Malhan has named these two structures Shakti and Shiva, the latter one of the principal deities of Hinduism and the former a female cosmic force often portrayed as Shiva’s consort.
Their energy and angular momentum values, plus their overall low metallicity on par with that of the “poor old heart”, makes Shakti and Shiva good candidates for some of the earliest ancestors of our Milky Way. Rix says: “Shakti and Shiva might be the first two additions to the ‘poor old heart’ of our Milky Way, initiating its growth towards a large galaxy.”
Several surveys that are either already ongoing or bound to start over the next couple of years promise relevant additional data, both spectra (SDSS-V, 4MOST) and precise distances (LSST/Rubin Observatory), should enable astronomers to make a firm decision on whether or not Shakti and Shiva are indeed a glimpse of our home galaxy's earliest prehistory.
JOURNAL
The Astrophysical Journal
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
Shiva and Shakti: Presumed Proto-Galactic Fragments in the Inner Milky Way
ARTICLE PUBLICATION DATE
21-Mar-2024
Secrets of the Van Allen belt revealed in new study
A challenge to space scientists to better understand our hazardous near-Earth space environment has been set in a new study led by the University of Birmingham.
The research represents the first step towards new theories and methods that will help scientists predict and analyse the behaviour of particles in space. It has implications for theoretical research, as well as for practical applications such as space weather forecasting.
The research focused on two bands of energetic particles in near earth space, referred to as the Radiation Belts, or the Van Allen Belts. These particles are trapped within the Earth’s magnetosphere and can damage electronics on satellites and spacecraft passing through, as well as posing risks to astronauts.
Understanding how these particles behave has been a goal for physicists and engineers for decades. Since the 1960s, researchers have used principles contained within ‘quasilinear models’ to explain how the charged particles move through space.
In the new study, however, researchers have found evidence that the standard theory might not apply as often as previously assumed. The team of 16 scientists, from institutions in the UK, USA and Finland, explored the limits of standard theories. The application of the quasilinear theory can seem straightforward, but in fact integrating it into space physics models in accordance with scientific measurements made in space is a delicate procedure. This paper breaks down the challenges behind this process.
The findings are published in a special edition of Frontiers in Astronomy and Space Sciences: “Editor’s Challenge in Space Physics: Solved and Unsolved Problems in Space Physics”.
Lead author, Dr Oliver Allanson, from the Space Environment and Radio Engineering (SERENE) Group at the University of Birmingham, said: “Gaining a better understanding of the behaviour of these particles is crucial for interpreting satellite data and for understanding the underlying physics of space environments.”
Researchers involved in the study are based in the UK at the Universities of Birmingham, Exeter, Northumbria, Warwick, St Andrews, and at the British Antarctic Survey; in the USA at the University of California at Los Angeles, University of Iowa and the US Air Force Research Lab, New Mexico; and in Finland at the University of Helsinki.
Next steps for the research will include an enhanced theoretical description based on the findings in this work, that can then be used in space weather models to forecast the behaviour of these hazardous particles in near-Earth space.
JOURNAL
Frontiers in Astronomy and Space Sciences
METHOD OF RESEARCH
Computational simulation/modeling
SUBJECT OF RESEARCH
Not applicable
ARTICLE TITLE
The challenge to understand the zoo of particle transport regimes during resonant wave-particle interactions for given survey-mode wave spectra
Heat to blame for space pebble demise
Pebbles are destroyed proportional to the peak temperature they reach along their orbit
SETI INSTITUTE
IMAGE:
THIS METEOROID BROKE UP BY THERMAL STRESSES JUST BEFORE ENTERING EARTH'S ATMOSPHERE, CREATING A CLUSTER OF METEORS OVER NORWAY ON OCTOBER 30, 2022, RECORDED BY ALLSKY7 STATION AMS119 OPERATED BY GAUSTABANEN AND STEINAR MIDTSKOGEN OF THE NORWAY METEOR NETWORK.
view moreCREDIT: MIKE HANKEY, AMERICAN METEOR SOCIETY
March 21, 2024, Mountain View, CA -- The dust of comets fills the space between the planets, collectively called the zodiacal cloud. Still, severe breakdown has reduced that dust in size so much that it now scatters sunlight efficiently, causing the faint glow in the night sky known as the "zodiacal light."
It was long thought that high-speed collisions pulverized the comet ejecta, but now a 45-member team of researchers reports, in a paper published online in the journal Icarus this week, that heat is to blame.
“Comets eject most debris as large sand-grain to pebble-sized particles, called meteoroids, that move in meteoroid streams and cause the visible meteors in our meteor showers,” says Dr. Peter Jenniskens, meteor astronomer at the SETI Institute. “In contrast, the zodiacal cloud is mostly composed of particles the size of tobacco smoke that even radars have difficulty detecting as meteors.”
Why do pebbles pulverize after they leave the comet?
“Meteor showers show us this loss of pebbles over time, because older showers tend to contain fewer bright meteors than young showers,” said Jenniskens. “We set out to investigate what is responsible.”
Jenniskens leads a NASA-sponsored global network called “CAMS” that monitors the night sky for meteors with low-light video security cameras. Most co-authors on the paper are the researchers and citizen scientists who built and operate the 15 CAMS camera networks in ten countries.
“We developed software that detects meteors in videos recorded from different locations and then triangulates their trajectory in the atmosphere,” said detection specialist Peter S. Gural. “Meteors arriving from the same direction each day belong to a meteor shower.”
Nightly maps showing from what direction those meteors arrive at Earth are at the website: https://meteorshowers.seti.org. After 13 years of observations, the combined maps were recently published as a book, “Atlas of Earth’s Meteor Showers”, an encyclopedia of information on each known meteor shower.
“As part of this work, we determined the age of meteor showers from how much they had dispersed,” says Stuart Pilorz of the SETI Institute, “and then examined how rapidly they were losing their large meteoroids compared to the smaller ones.”
To investigate what is responsible, the team examined of how close those streams came to the Sun. If collisions were to blame, then the pebbles were expected to be destroyed faster directly proportionally to their proximity to the Sun.
“Because there is more comet dust closer to the Sun, we had expected collisions there would pulverize the pebbles that much faster,” says Jenniskens. “Instead, we found that the pebbles survived better than expected.”
The research team concluded that, instead, the pebbles are destroyed proportional to the peak temperature they reach along their orbit. Thermal stresses are likely to blame for breaking up the large meteoroids near Earth, and all the way to the orbit of Mercury, while deep inside the orbit of Mercury the particles are heated so much that they fall apart from losing material.
“Here at Earth, we sometimes see that process in action when in a short time of say 10 seconds we detect ten or twenty meteors in part of the sky, a meteor cluster, the result of a meteoroid having fallen apart by thermal stresses just before entering Earth’s atmosphere,” says Jenniskens.
Manuscript online at: https://authors.elsevier.com/sd/article/S0019-1035(24)00093-9
About the SETI Institute
Founded in 1984, the SETI Institute is a non-profit, multi-disciplinary research and education organization whose mission is to lead humanity’s quest to understand the origins and prevalence of life and intelligence in the Universe and to share that knowledge with the world. Our research encompasses the physical and biological sciences and leverages expertise in data analytics, machine learning and advanced signal detection technologies. The SETI Institute is a distinguished research partner for industry, academia and government agencies, including NASA and NSF.
Same meteor cluster from a different perspective.
CREDIT
Steinar Midtskogen and Mike Hankey
JOURNAL
Icarus
ARTICLE TITLE
Lifetime of cm-sized zodiacal dust from the physical and dynamical evolution of meteoroid streams
ARTICLE PUBLICATION DATE
1-Jun-2024
No comments:
Post a Comment