New Discovery Challenges Dark Matter, Stellar Acceleration Models

New Hypervelocity Binary Star Challenges Dark Matter, Stellar Acceleration Models

PB3877 is a hyper-velocity wide binary star zooming through the outskirts of the Milky Way galaxy. This image shows its current location as well as our Sun.

Astronomers have discovered a hypervelocity binary star that challenges dark matter and stellar acceleration models.

A team of astronomers at the Friedrich Alexander University led by Péter Németh has discovered a binary star moving nearly at the escape velocity of our galaxy. There are about two dozen so-called hypervelocity stars known to be escaping the galaxy. While all of them are single stars, PB3877 is the first wide binary star found to travel at such a high speed. Additionally, the results of the new study challenge the commonly accepted scenario that hypervelocity stars are accelerated by the supermassive black hole at the galactic center. The findings are published in the Astrophysical Journal Letters.

The team, in collaboration with researchers from the California Institute of Technology, showed the binary cannot originate from the Galactic Center, and no other mechanism is known that is able to accelerate a wide binary to such a high velocity without disrupting it. They, therefore, hypothesized there must be a lot of dark matter to keep the star bound to the Milky Way galaxy; or the binary star, PB3877, could be an intruder that has been born in another galaxy and may or may not leave the Milky Way again.

PB3877 was first reported to be a hyper-velocity, hot compact star, when it was discovered from the Sloan Digital Sky-Survey (SDSS) data in 2011. New spectroscopic observations were done with the 10-meter (33-foot) Keck II telescope at W. M. Keck Observatory on Maunakea, Hawaii, and with the 8.2-meter (27-foot) Very Large Telescope (VLT) of the European Southern Observatory (ESO) in Chile. Caltech astronomers Thomas Kupfer and Felix Fürst observed PB3877 with the ESI Instrument fitted on the Keck II telescope.

“When we looked at the new data, much to our surprise, we found weak absorption lines that could not come from the hot star,” Kupfer said. “The cool companion, just like the hot primary, shows a high radial velocity. Hence, the two stars form a binary system, which is the first hyper-velocity wide binary candidate.”

The surface of the hot compact star is more than five times hotter than the Sun, while the companion is a thousand degrees cooler than our Sun. The system was determined to be 18,000 light-years away. The mass of the hot compact star is only half of the mass of our Sun, and the companion is .7 times the mass of the Sun.

“We studied hyper-velocity stars since 2005, the year of discovery of the first three,” said team member Ulrich Heber. “In the meantime, about two dozen have been found, but all are single, none has a companion directly visible in its spectrum.”

The center of our galaxy hosts a supermassive black hole that can accelerate and eject stars from the galaxy by disrupting an original binary star. Hence, most hyper-velocity stars are believed to originate from the galactic center.

“From our calculations, we can exclude the Galactic Center as the place of origin, because its trajectory never came close to it,” said team member Eva Ziegerer, a specialist in stellar kinematics who collected the astrometry data and reconstructed the orbit of the binary. “Other ejection mechanisms, such as stellar collisions and a supernova explosion have been proposed, but all of them would lead to the disruption of a wide binary.”

“PB3877 may be an intruder from another galaxy,” Németh said. “In that case its prolonged gradual acceleration would not harm its integrity. The outskirts of our Galaxy contain various stellar streams that are believed to be the remnants of dwarf galaxies that were torn to shreds by the strong tidal force of the Milky Way.”

Unfortunately, the available data do not allow us to make a connection to any of the known streams. Therefore, the origin of the binary remains unclear and so is its future. Whether or not the system remains bound to the Galaxy depends on the amount of dark matter in the Galaxy. Therefore, the mere existence of this binary puts pressure on our models and on our current understanding of dark matter in the Milky Way.

“We used different mass models to calculate the probability that the star will actually remain bound to the Galaxy. Only for the most massive Galaxy model this is the case. This makes PB3877 an excellent target to probe dark matter halo models,” said Andreas Irrgang, research associate at the Dr. Karl Remeis-Observatory.

The research continues with high-resolution spectroscopy to confirm the orbital properties of PB3877 and with a photometric follow-up to search for variability. “By finding further stars or binaries on similar orbits would indicate an external origin. Therefore, our quest for similar strangers will continue,” Németh said.

The W. M. Keck Observatory operates the largest, most scientifically productive telescopes on Earth. The two, 10-meter optical/infrared telescopes near the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs, and world-leading laser guide star adaptive optics systems.

ESI (Echellette Spectrograph and Imager) is a medium-resolution visible-light spectrograph that records spectra from 0.39 to 1.1 microns in each exposure. Built at UCO/Lick Observatory by a team led by Prof. Joe Miller, ESI also has a low-resolution mode and can image in a 2 x 8 arc-min field of view. An upgrade provided an integral field unit that can provide spectra everywhere across a small, 5.7 x 4.0 arc-sec field. Astronomers have found a number of uses for ESI, from observing the cosmological effects of weak gravitational lensing to searching for the most metal-poor stars in our galaxy.

Reference: “AN EXTREMELY FAST HALO HOT SUBDWARF STAR IN A WIDE BINARY SYSTEM” by Péter Németh, Eva Ziegerer, Andreas Irrgang, Stephan Geier, Felix Fürst, Thomas Kupfer and Ulrich Heber, 11 April 2016, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8205/821/1/L13

7 Comments on "New Discovery Challenges Dark Matter, Stellar Acceleration Models"

  1. The notion of dark matter as a weakly interacting clump of stuff that travels with the matter is incorrect. Dark matter fills ’empty’ space. Dark matter strongly interacts with matter. Dark matter is displaced by matter.

    [0903.3802] The Milky Way’s dark matter halo appears to be lopsided

    “the emerging picture of the dark matter halo of the Milky Way is dominantly lopsided in nature.”

    The Milky Way’s halo is not a clump of dark matter traveling along with the Milky Way. The Milky Way’s halo is lopsided due to the matter in the Milky Way moving through and displacing the dark matter, analogous to a submarine moving through and displacing the water.

    What physicists mistake for the density of the dark matter is actually the state of displacement of the dark matter. Physicists think they are determining the density of the dark matter by how much it and the matter curve spacetime. What they fail to realize is the state of displacement of the dark matter is curved spacetime.

  2. There is no such thing as dark matter and black holes it is electricity in a plasma universe

  3. David Reichard | April 14, 2016 at 6:42 pm | Reply

    I am not a scientist:however,it seems fairly obvious that for matter to displace dark matter there must be a force between them.Also,it must be stronger than any gravitational attraction between them.Has mpc755 any suggested mechanism or force to explain this?

    • Dark matter has mass, physically occupies three dimensional space and is physically displaced by the particles of matter which exist in it and move through it.

      ‘NASA’s Gravity Probe B Confirms Two Einstein Space-Time Theories’

      “”Imagine the Earth as if it were immersed in honey. As the planet rotates, the honey around it would swirl, and it’s the same with space and time,” said Francis Everitt, GP-B principal investigator at Stanford University.”

      Honey has mass and so does the dark matter. The ‘swirl’ is the state of displacement of the dark matter.

      What is referred to geometrically as curved spacetime physically exists in nature as the state of displacement of the dark matter.

      The state of displacement of the dark matter is curved spacetime.

      The state of displacement of the dark matter is gravity.

      The dark matter displaced by the Earth pushing back and exerting inward pressure toward the Earth is gravity.

      • mpc,
        why is there 5x more dark matter then ordinary baryons?
        I mean if your analogy with honey has to work, then honey has 5x bigger density, then “our” vacuum. Means intergalactic space would be extremely dense.

        • Dark matter fills ’empty’ space. Dark matter exists everywhere particles of matter do not. Where the particles of matter exist the dark matter has been displaced.

          Displaced dark matter pushing back and exerting pressure toward matter is gravity.

      • I believe there is no frame-dragging effect of gravity on mass, only on electromagnetic energy!
        Curiously, the Lense-Thirring effect in Gravity Probe B has the same value than the geodetic effect of the Earth around the Sun.
        NASA error?
        An interesting experiment!
        Understanding Gravity Probe-B experiment without math

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