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Exactly how massive is the Milky Way?

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Exactly how massive is the Milky Way?


Artist depiction of the Milky Way galaxy. Credit score: Andrew Z. Colvin

How do you weigh a galaxy? It is an astronomical problem, notably if it is the galaxy you name house. It turns on the market are a number of methods to get a deal with on the mass of the Milky Way, and a latest research posted on the arXiv pre-print server summarizes these strategies to current the perfect worth.

One technique is to have a look at the movement of stars within the galaxy. Most Milky Way stars comply with a roughly round path across the galactic center. Simply as planets orbit the Solar, stars orbit the galaxy. Since gravity is the power holding stars of their orbit, you should utilize a star’s pace and distance from the middle to find out the mass inside its orbit. Not all stars have round orbits, however they do on common. So you may plot the pace vs. distance from the middle for recognized stars, and get what is named the rotation curve. Measurements of this curve within the Milky Way and different galaxies had been the primary proof that galaxies had way more mass than might be accounted for by seen stars, resulting in the concept of dark matter.

One of many issues with the rotation curve technique is that we will solely measure stars to a sure distance. We now know that the majority of our galaxy’s mass is not concentrated on the middle, however moderately extends outward right into a galactic halo. We will estimate the mass of the halo from the rotation curve, however we will additionally have a look at the movement of globular clusters.

Globular clusters are brilliant dense clusters of stars. Since stars inside a globular cluster are gravitationally certain, these clusters transfer across the galaxy like a single object. They’re present in a sphere surrounding the Milky Way, so measuring their movement helps us measure the mass of the galactic halo.

Numerous strategies for massing the Milky Way. Credit score: Bobylev and Bajkova

To measure the outer area of the galactic halo, we will have a look at the movement of satellite galaxies such because the Magellanic Clouds. There are about 60 small galaxies inside about 1.4 million light-years of the Milky Way. Not all of them are in orbit round our galaxy, however lots of them are. Since they lay outdoors our galactic halo, their orbital motions are decided by all of our galaxy’s mass. The one draw back of this method is that with just a few dozen orbiting galaxies, the consequence is not notably correct.

All of those approaches calculate the mass of the Milky Way from orbital movement. There are just a few strategies that do not depend on the orbital movement. One among these is to have a look at the tidal plumes of dwarf galaxies. Within the historical past of our galaxy, there are some globular clusters and dwarf galaxies that strayed too near the central area of the Milky Way and had been ripped aside by tidal forces. The remnants of those galaxies type a stream of stars, such because the Sagittarius stream. By calculating the movement of those streams we will estimate galactic mass.

One other method is to have a look at stars leaving our galaxy. Often a star could have a close to miss with one other star and acquire sufficient velocity to flee our galaxy. For the reason that escape velocity depends upon galactic mass, a statistical measure of escaping stars provides a mass for the galaxy.

Lastly, we will have a look at the local group of galaxies. This consists of the Andromeda galaxy and its satellite galaxies. Our local group is gravitationally remoted from extra distant galaxy clusters, so trying on the equilibrium state of the local group provides us a deal with on its general mass and the mass of the Milky Way.

Every of those approaches has its personal benefits and ranges of accuracy. None of them are the ultimate say on their very own. On this newest work, the group took a statistical common of assorted strategies and derived what we would name the perfect worth for the mass of our galaxy. The worth they decided was a trillion solar lots, give or take just a few hundred billion solar masses.

Extra data:
V. V. Bobylev et al, Assessment of present estimates of the Galaxy mass, arXiv (2023). DOI: 10.48550/arxiv.2305.18408

Journal data:
arXiv


Offered by
Universe Today


Quotation:
Precisely how huge is the Milky Way? (2023, June 2)
retrieved 2 June 2023
from https://phys.org/information/2023-06-massive-milky.html

This doc is topic to copyright. Other than any honest dealing for the aim of personal research or analysis, no
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