Our Milky Way Galaxy is rich in dark matter. The problem is, we can\u2019t see where it\u2019s distributed because, well, it\u2019s dark. We also don\u2019t completely understand how it\u2019s distributed\u2014in clumps or what? A team at the University of Alabama-Huntsville has figured out a way to use solitary pulsars to map this stuff and unveil its effect on the galaxy.<\/p>\n
<\/p>\n A technique developed by Dr. Sukanya Chakrabarti and her team is based on some unique characteristics of pulsars. In addition, it uses the presence of a strange wobble of our galaxy. It seems to be induced by interactions with dwarf galaxies such as the Large Magellanic Cloud. That wobble has a connection to the amount of dark matter in the galaxy, and it turns out that pulsars can help map it.<\/p>\n Pulsars are the corpses of massive stars. After they explode as supernovae, what remains is a rapidly spinning compressed stellar core. These beasts sport incredibly strong magnetic fields. Those fields twist and coil up as they spin many times per second and send high-speed particles out to space. That causes the pulsar to lose energy. Combined with friction produced by the motions of the twisted magnetic field, the pulsar slows down ever so slightly in a process called \u201cmagnetic braking\u201d. Scientists have worked for years to model this process to understand the behavior of pulsars.<\/p>\n The Milky Way Galaxy\u2019s behavior is another part of the dark matter mapping puzzle. Astronomers know it has a substantial component of dark matter that appears not to be evenly spread out. The actual distribution of that mass of dark matter leads to some interesting effects, according to Chakrabarti. \u201cIn my earlier work, I used computer simulations to show that since the Milky Way interacts with dwarf galaxies, stars in the Milky Way feel a very different tug from gravity if they\u2019re below the disk or above the disk,\u201d she said. \u201cThe Large Magellanic Cloud (LMC)\u2013a biggish dwarf galaxy\u2013orbits our own galaxy, and when it passes near the Milky Way, it can pull some of the mass in the galactic disk towards it\u2013leading to a lopsided galaxy with more mass on one side, so it feels the gravity more strongly on one side.\u201d<\/p>\n Chakrabarti compared this interesting galaxy \u201cwobble\u201d to the way a toddler walks\u2013not entirely balanced yet. That wobble affects stars, including pulsars. And it turns out that the different tugs of gravity caused by the distribution of dark matter affects their spindown rates. \u201cSo this asymmetry or disproportionate effect in the pulsar accelerations that arises from the pull of the LMC is something that we were expecting to see,\u201d said Chakrabarti. In other words, those tugs of gravity by dark matter give away its distribution and possibly its density throughout the Galaxy.<\/p>\n Chakrabarti and her team previously pioneered the use of binary pulsars to map dark matter in the Galaxy. It turns out that magnetic braking doesn\u2019t affect the orbits of pulsars in binary systems. That makes them useful to measure the amount and distribution of dark matter in the Milky Way. So, the team measured the acceleration of pulsar spin rates due to the effect of the Milky Way\u2019s gravitational potential. That work showed it\u2019s possible to map the galaxy\u2019s gravitational field with data points from more binary pulsars. That includes clumps of galactic dark matter. However, there\u2019s a problem. There are a lot of singular pulsars. There had to be a way to use them, too. And that brings us back to the team\u2019s modeling of pulsar spindown.<\/p>\n \u201cBecause of this spindown, we were initially\u2013in 2021 and in our follow-up 2024 paper\u2013forced to use only pulsars in binary systems to calculate accelerations because the orbits aren\u2019t affected by magnetic braking,\u201d said team member Tom Donlon. \u201cWith our new technique, we are able to estimate the amount of magnetic braking with high accuracy, which allows us to also use individual pulsars to obtain accelerations.\u201d<\/p>\n Adding more \u201cpoint source\u201d measurements with single pulsars, Chakrabarti\u2019s team predicts that it should eventually be possible to determine a much more accurate understanding of the distribution of dark matter in the Milky Way. \u201cIn essence, these new techniques now enable measurements of very small accelerations that arise from the pull of dark matter in the galaxy,\u201d Chakrabarti said. \u201cIn the astronomy community, we have been able to measure the large accelerations produced by black holes around visible stars and stars near the galactic center for some time now. We can now move beyond the measurement of large accelerations to measurements of tiny accelerations at the level of about 10 cm\/s\/decade. 10 cm\/s is the speed of a crawling baby.\u201d<\/p>\n UAH Breakthrough Enables the Measurement of Local Dark Matter Density Using Direct Acceleration Measurements for the First TimeDark Matter Mapping and Pulsars<\/h3>\n
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Building on Previous Work<\/h3>\n
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Need More Data<\/h3>\n
For More Information<\/h4>\n
Empirical Modeling of Magnetic Braking in Millisecond Pulsars to Measure the Local Dark Matter Density and Effects of Orbiting Satellite Galaxies
Galactic Structure From Binary Pulsar Accelerations: Beyond Smooth Models<\/p>\nLike this:<\/h3>\n