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  • richardmitnick 10:17 am on February 28, 2020 Permalink | Reply
    Tags: "Stunning Images Capture Cosmic Ray Tracks", , , Cosmic rays are made mostly from the result of supernovae explosions and reaching us at nearly the speed of light., Losing more energy as it travels round and round the particle creates the curious circles in the images called “loopers.”, Particles with no electric charge always move in straight lines; however they cannot even be seen by the detector., , star, STAR is only able to track charged particles which get pulled by the the detector’s magnetic field creating a curve., The “heart” of the STAR detector is its Time Projection Chamber- a four-meter-wide 4.2-meter-long cylinder filled with a gas mixture of argon and methane.   

    From Brookhaven National Lab: “Stunning Images Capture Cosmic Ray Tracks” 

    From Brookhaven National Lab

    February 26, 2020
    Erika Peters
    epeters@bnl.gov

    The beauty in science shines through at RHIC’s STAR detector [below] and makes a cosmic connection.

    1
    To help calibrate the STAR detector, physicists track and capture images of showers of cosmic rays streaming from space. Can you pick out which image shows tracks from a particle collision at RHIC (hint: the collision occurred at the center of the detector)?

    These images capture the movement and collisions of “cosmic rays”—mysterious particles originating somewhere in deep space—as they stream through the STAR detector at the Relativistic Heavy Ion Collider (RHIC) [below]. The results are profoundly beautiful.

    The rays, made mostly from the result of supernovae explosions and reaching us at nearly the speed of light, are not just things of beauty. Physicists conducting research at RHIC—a U.S. Department of Energy Office of Science user facility for nuclear physics research at Brookhaven National Laboratory—use their signals as a tool for calibrating the massive detectors collecting data for the collider’s physics experiments.

    The “heart” of the STAR detector is its Time Projection Chamber, a four-meter-wide, 4.2-meter-long cylinder filled with a gas mixture of argon and methane, explained Irakli Chakaberia, a research scientist on the STAR experiment. Each of the detector’s endcaps has 12 “sectors,” each with 72 padrows that sense electric charge, acting as a camera that can capture over 2,000 images a second. Tracing the trails of a shower of cosmic rays passing through the gas helps scientists know if their detector components are all working correctly.

    The higher the energy of the original cosmic track, the bigger the proliferation of the shower, creating what appear to be more “lively” images with many tracks in the chamber. How linear the path appears helps show the particle’s speed—the faster the particle moves, the straighter its path. Particles with no electric charge always move in straight lines; however, they cannot even be seen by the detector. STAR is only able to track charged particles, which get pulled by the the detector’s magnetic field, creating a curve. Those with lower momentum, called “soft” particles, are pulled more by the detector’s magnets and curve more than faster ones.

    “Based on the direction of the curve, we can tell whether the particle is positively or negatively charged,” Chakaberia said.

    When a cosmic ray particle collides with an atom of the gas in the detector, it might produce a “softer” particle moving with lower energy. Losing more energy as it travels round and round, the particle creates the curious circles in the images called “loopers.” Sometimes in the initial cascade, there are particles “soft” enough to loop around on their own.

    Even though physicists use powerful computers to analyze data from STAR, “nothing replaces an actual human eye,” Chakaberia said.

    “For example, when looking at some cosmic data, there was a case where tens of tracks were reconstructed in a single detector sector,” Chakaberia said. “This could, in principle, happen, but after checking the event display by eye it was obvious that it was a result of noise in that sector. The software couldn’t distinguish between the noise and real events to some degree. So these track displays help a lot to figure out what’s going on.”

    After cosmic rays have done their job testing and calibrating, STAR is ready to capture the thousands of tracks produced by ion collisions at RHIC. To increase the chance of two ions colliding, billions are aimed at each other with each pass through the detector, and the tracks reveal more of the beauty and the art that can be found in science. In this case, all the particle tracks emerge from the center of the detector, where the collision takes place. (Can you find the one ion-collision event in the images shown here?)

    Nuclear physicists analyze the ion-collision tracks to learn about a remarkable state of matter created in RHIC’s heavy-ion collisions. This “quark-gluon plasma” is a soup of particles that mimics what the universe was like just after the Big Bang. It’s a kind of cosmic connection: Scientists use a detector calibrated by particles from the cosmos to learn more about the marvelous and mystifying universe that created them.

    Research at RHIC/STAR is funded by the DOE Office of Science and by funders of the STAR collaboration listed here.

    See the full article here .


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  • richardmitnick 1:07 pm on May 4, 2017 Permalink | Reply
    Tags: , , , , , Run away, star   

    From astrobites: “Run away, star” 

    Astrobites bloc

    Astrobites

    May 4, 2017
    Philipp Plewa

    Title: Hypervelocity runaways from the Large Magellanic Cloud
    Authors: D. Boubert, D. Erkal, N.W. Evans, R.G. Izzard
    First Author’s Institution: Institute of Astronomy, University of Cambridge
    1
    Status: Published in MNRAS, open access

    The fastest known stars in the Galaxy are the ones orbiting the supermassive black hole in its very center. At the time of closest approach to the black hole, these stars can reach speeds on the order of 10000 km/s or more. Their origin is suspected to be the Hills mechanism: If a binary star system is scattered into the vicinity of the black hole, by gravitational interaction one of the companion stars can get captured on a close orbit, while the other is ejected.

    A few extremely fast-moving stars have also been discovered in the Galactic halo, traveling at speeds exceeding 500 km/s, some of which could even escape the Milky Way. Presumably, these hypervelocity stars are the Hills stars now outbound from the Galactic center, although alternative explanations have been proposed as well. The authors of today’s paper explore yet another scenario: Could the Milky Way’s hypervelocity stars originate from the Large Magellanic Cloud (LMC)?

    Large Magellanic Cloud. Adrian Pingstone December 2003

    To answer this question, the authors first generate a synthetic population of stars, accounting for the specific star formation history of the LMC, while giving special attention to modeling the evolution of stellar binaries. They then identify potential runaway stars that are ejected from binary systems after supernova explosions. These stars (or stellar remnants) can receive kicks up to several 100 km/s, in particular if a supernova occurs in a previously close, interacting massive binary system. This can happen in the Milky Way too, but because the LMC is significantly less massive, less extreme kicks are enough to accelerate stars to escape velocity.

    As a next step, the identified runaway stars are placed in a joint, large-scale dynamical simulation of the LMC and Milky Way. Performing this simulation makes it possible to find out which stars could end up in which present-day locations and with what velocities. Finally, the authors compute the observable properties of all stars in their simulation, to check the feasibility of detecting a population of LMC runaways in current or future surveys.

    2
    Figure 1: The expected on-sky distribution of LMC runaway stars at the present day. Most of them have evolved into stellar remnants, but still thousands of main-sequence stars could have survived. The known hypervelocity stars are marked by red crosses, but the area below the dashed line in particular has not yet been thoroughly searched for more. An animated version of this figure is available at https://youtu.be/eE-1JXBP1J8. (Figure 2 from the paper, with the dashed line added to indicate the celestial equator.)

    The population of LMC runaways they predict is consistent with several recent observations. Firstly, the brightest stars in the LMC, which are massive stars most likely to either have a companion or to be runaway stars, show motions that are generally matching expectations. Secondly, there exist young stars in the outskirts of the LMC, far away from regions of star formation. Thirdly, an unusually large fraction of massive main-sequence stars formed in the leading arm of the LMC appear to be single stars.

    But could the Milky Way’s hypervelocity stars actually be LMC runaways? The authors call it a realistic possibility. They estimate that tens of thousands of stars have escaped the LMC over the last 2 Gyr in total and that thousands of them could have survived as observable, main-sequence stars until today. Many of them could also escape the Milky Way and would be classified as hypervelocity stars.

    The latest, most extensive searches for hypervelocity stars have unfortunately not yet had a chance of finding the the majority of hypervelocity runaways from the LMC, because of missing sky coverage in the Sloan Digital Sky Survey (SDSS).

    SDSS Telescope at Apache Point Observatory, NM, USA

    But the few hypervelocity stars that have been found so far are clustered in a region of the sky that extends along the projected path of the LMC, where detections of LMC runaway stars would be anticipated, and they have velocities and distances compatible with an LMC origin (Figure 1).

    However, the known hypervelocity stars are somewhat more massive than the predicted runaways (more than three solar masses). This discrepancy with respect to observations could be resolved, if the assumptions going into the adopted binary evolution model were to change. Most importantly, it would be necessary to adjust or better constrain the parameters describing the common envelope phase, much about which is still unknown.

    The authors conclude that at least some LMC runaway stars, being unavoidable by-products of normal star formation, must classify as Milky Way hypervelocity stars. If the Gaia mission can help discover more than only a few runaway stars escaping the LMC, hypervelocity stars will remain special but maybe not as rare as they seem now, and we can look forward to getting a much better opportunity of understanding all their various possible origins.

    ESA/GAIA satellite

    See the full article here .

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    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.
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