Reduce the mass of the milky way

Since the birth of modern astronomy, scientists have sought to determine the extent of the Milky Way and to learn more about its structure, formation, and evolution. Currently, astronomers estimate that it has a diameter of 100,000 to 180,000 light-years and that it consists of 100 to 400 billion stars, although some estimates indicate that it could reach 1 000 billion.

And yet, even after decades of research and observations, our astronomers in the galaxy still do not know much. For example, they are still trying to determine the size of the Milky Way, and estimates vary considerably. In a new study, a team of international scientists presents a new method of weighing the galaxy based on the dynamics of satellite galaxies of the Milky Way.

The study entitled "The Mass of the Milky Way from the Dynamics of Satellites" appeared recently in Monthly Notices from the Royal Astronomical Society. The study was led by Thomas Callingham, of the Institute of Computational Cosmology at the University of Durham, and included members of the Massachusetts Institute of Technology (MIT), the Heidelberg Institute of # 39; theoretical studies and several universities.

As they indicate in their study, the mass of the Milky Way is fundamental to our understanding of astrophysics. Not only is it important to place our galaxy in the context of the galaxy population in general, but it also plays a major role in addressing some of the greatest mysteries that arise from our current astrophysical and cosmological theories.

These include the complexities of galaxy formation, divergences with the current Lambda Cold Dark Matter model (Lambda CDM), alternative theories about the nature of dark matter and the large-scale structure of the universe. In addition, a number of factors have impeded previous studies, including the fact that the dark matter halo of the Milky Way (which constitutes the bulk of its mass) can not be observed directly.

Another major problem is the fact that it is difficult to measure the extent and mass of the Milky Way because we are there. As a result, previous studies that have attempted to infer mass from our galaxy have resulted in mass estimates ranging from about 500 billion to 2.5 trillion times the mass of our sun (solar masses). As Callingham explained to the Universe today by email, a refined approach was needed:

"The majority of the galaxy is in its dark matter halo, which can not be directly observed, but instead we deduce its properties by observing various dynamic tracers that sense the gravitational effects of dark matter – stellar populations, clusters globular, vapor and satellite galaxies, most of which are at the center of a galaxy in the galactic disk (about 10kpc) and in the stellar halo (~ 15kpc), which can give a good estimate of the mass of the region 200kpc, and for this reason we chose to focus on satellite galaxies, one of the only tracers to probe these outer parts of the galaxy. "

For the purposes of their study, the team relied on data from the second version of data from the Gaia satellite (DR2 version) to impose better constraints on the mass of the Milky Way. Gaia's mission, which has provided more information than ever on our galaxy, includes the relative position and movement of countless stars in the Milky Way – including those found in satellite galaxies. As Callingham has pointed out, this has proved very useful in limiting the mass of the Milky Way:

"We compare the energy and angular momentum orbital properties of MW satellite galaxies with those of simulations, using the latest observations of MWs satellites from the recent Gaia DR2 data set and a sample of appropriate satellite galaxies and galaxies from EAGLE simulations: a foreground simulation was carried out at Durham with a large volume and a complete hydrodynamic baryonic physics. "

The EAGLE software (Evolution and Assembly of GaLaxies and their Environments), developed by the Institute of Computational Cosmology at the University of Durham, models the formation of structures in a cosmological volume of 100 megaparsecs (more than 300 million 'light years). However, the use of this software to infer the mass of the Milky Way presented some challenges.

"A challenge to this is the limited sample of MW size galaxies in EAGLE (or even any simulation)," said Callingham. "To help with that, we use a mass scale relationship to scale our total sample of galaxies to the same mass, which allows us to use our data set more efficiently and effectively. dramatically improves our statistics Our method was then rigorously tested Galaxies simulated from the EAGLE and Auriga simulations – an independent suite of high-resolution simulations, which ensures that our mass estimate is robust and includes realistic errors (something that the domain sometimes encounters because of analytical hypotheses).

From this they found that the total mass of halos of the Milky Way was about 1.04 x 1012 (more than 1 000 billion) solar masses, with an error margin of 20 %. This estimate imposes much more stringent constraints on the mass of the Milky Way than the previous estimates and could have important implications in the fields of astronomy, astrophysics and cosmology. As Callingham summarized:

"A tighter mass estimate can be used in many ways." In galaxy modeling, the DM halo is the backdrop on which stellar components are adapted. </ P> <p> Many methods to probe the nature of the DM, such as the structure of the DM halo, the density of DM on Earth for direct detection depends on the mass of MW.The mass can also be used to predict the number of satellite galaxies around the MW we expect. "

In addition to providing astronomers with refined measurements of the mass of the Milky Way – which will greatly contribute to our understanding of its size, extent and satellite galaxy population – this study also has implications for our understanding of Universe as a whole. In addition, it is another revolutionary study made possible thanks to the second version of Gaia.

The third version of Gaia's data is expected to take place at the end of 2020, the final catalog being published in the 2020s. In the meantime, an extension has already been approved for the Gaia mission, which will remain operational until the end of 2020. (to be confirmed at the end of this year).

Explore more:
How does one weigh a galaxy? Especially the one in which you are?

More information:
The mass of the Milky Way from the dynamics of satellites. arxiv.org/pdf/1808.10456.pdf