The wrinkles in the Milky Way are shown, along with the tidal debris from the Sagittarius dwarf system. The pulses analyzed by Chakrabarti et al 2021 to calculate Galactic accelerations are shown in the insert. Credit: IAS; Dana Berry
It is known that the expansion of the universe is accelerating due to a mysterious dark energy. Within galaxies, stars also experience an acceleration, although this is due to a combination of dark matter and star density. In a new study to be published in Astrophysical Journal Letters, researchers now have the first direct measurement of the average acceleration in our home system, the Milky Way.
Led by Sukanya Chakrabarti at the Institute for Advanced Study, in collaboration with Rochester Institute of Technology, University of Rochester and University of Wisconsin-Milwaukee, the team used pulsar data to clock the radial and vertical accelerations of stars inside and outside the galactic plane. Based on these new high-precision measurements and the known amount of visible matter in the galaxy, researchers were then able to calculate the Milky Way density of the Milky Way without making the usual assumption that the galaxy is in a stable state.
“Our analysis not only gives us the first measurement of the small accelerations that stars experience in the galaxy, but also offers the possibility of expanding this work to understand the nature of dark matter and ultimately dark energy on a larger scale,” said Chakrabarti. , the lead author of the article and a current member and IBM Einstein Fellow at the Institute for Advanced Study.
Stars flush hundreds of kilometers per second through the galaxy, but this study indicates that the change in their velocities takes place at a literal snail’s pace – a few centimeters per second, which is about the same speed as a crawling baby. To detect this subtle motion, the research team relies on the extremely precise time capability of pulses widely distributed across the galactic plane and the halo – a diffuse spherical region surrounding the galaxy.
“By utilizing the unique properties of pulses, we were able to measure very small accelerations in the galaxy. Our work opens a new window in galactic dynamics, ”said co-author Philip Chang of the University of Wisconsin-Milwaukee.
The halo, which extends about 300,000 light-years from the galactic center, can provide important tips for understanding dark matter, which makes up about 90 percent of the star’s mass and is highly concentrated above and below the star-dense galactic plane. Star motion in this particular region – a primary focus of this study – may be influenced by dark matter. Using the local density measurements obtained through this study, researchers will now have a better idea of how and where to look for dark matter.
While previous studies have assumed a state of galactic equilibrium to calculate the average mass density, this research is based on the natural, non-equilibrium state of the galaxy. One can analyze it by the difference between the surface of a pond before and after the casting of a stone. By offsetting the “ripples”, the team was able to obtain a more accurate picture of reality. Although the Milky Way in this case, rather than rocks, is affected by a turbulent history of galactic mergers and is still disturbed by external dwarf systems such as the Small and Large Magellanic Clouds. As a result, stars do not have flat orbits and tend to follow a path similar to that of a skewed vinyl record that intersects above and below the galactic plane. One of the most important factors that made this direct observation approach possible was the use of pulsar data compiled from international collaborations, including NANOGrav (North American Nanohertz Observatory for Gravity Waves) which collects data from the Green Bank and Arecibo telescopes obtained.
This distinctive paper expands on the work of Jan H. Oort (1932); John Bahcall (1984); Kuijken & Gilmore (1989); Holmberg & Flynn (2000); and Jo Bovy & Scott Tremaine (2012) to calculate the average mass density in the galactic plane (Oortlimit) and local density of dark matter. IAS scholars, including Oort, Bahcall, Bovy, Tremaine, and Chakrabarti, have played an important role in advancing this area of research.
“Astronomers have been measuring the positions and velocities of stars for centuries, but this gives only a glimpse of the complex dynamic behavior of the Milky Way galaxy,” he said. Scott Tremaine, Professor Emeritus at the Institute for Advanced Study. ‘The accelerations measured by Chakrabarti and her associates are directly caused by the gravitational forces of matter in the galaxy, both visible and dark, thus providing a new and promising window for the distribution and composition of matter in the galaxy and the universe. ”
This particular article will enable a wide range of future studies. Accurate measurements of accelerations will soon be possible using the complementary radial velocity method developed by Chakrabarti earlier this year, which measures the change in velocity of high-precision stars. This work will also allow for more detailed simulations of the Milky Way, improve the constraints on general relativity, and provide clues in the search for dark matter. Extensions of this method we can finally also measure the cosmic acceleration directly.
Although a direct picture of our home system – similar to that of Earth taken by the Apollo astronauts – is not yet possible, this study provided essential new details to help predict the dynamic organization of the galaxy from within.
Reference: “A Measurement of the Mass Density of the Galactic Level of Binary Pulsar Accelerations” accepted by Sukanya Chakrabarti, Philip Chang, Michael T. Lam, Sarah J. Vigeland, Alice C. Quillen, Astrophysical Magazine Letters.
arXiv: 2010.04018
Meeting: 237th meeting of the American Astronomical Society