THE ANDROMEDA GALAXY IS SLIGHTLY LESS MASSIVE THAN THE MILKY WAY

A new technique for measuring the mass of galaxies has been applied to our closest galactic neighbour - and it has found that the Andromeda galaxy is roughly the same size as the Milky Way, and not two to three times bigger as was previously thought.

The new measurement was obtained by a technique that calculates the speed required to escape the gravitational pull of a galaxy, or escape velocity. 

The escape velocity for Andromeda is about 470 (+- 40) km/s while our galaxy, the Milky Way has an escape velocity of about 550km/s. Ths puts the mass of Andromeda at 1.2 trillion solar mass versus the Milky Way's 1.5-2 trillion suns. 

This research is lead astrophysicist Prajwal Kafle from the International Centre for Radio Astronomy Research together with his team. 

While giving to the fact that it is hard to measure the parameters of our galaxy as we are inside it, improvements in our measurements will continue to revise the parameters of both Andromeda and Milky Way in the future. 

Source: Science Alert https://www.sciencealert.com/andromeda-galaxy-much-smaller-than-thought-same-size-milky-way

A 2018 research suggests that our galaxy is double in extension than the conventional 100,000 light years. 

Recent research has doubled the Milky Way's span to perhaps 200,000 light-years, showing that while the population of stars grows less dense in our galaxy's outer rim, a gauzy scattering stretches well past what scientists had previously observed.

Researchers made the find after analyzing the abundances of metals (heavy elements) in stars, also known as their metallicities using the survey data from the Apache Point Observatory Galactic Evolution Experiment (APOGEE) and the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), which collect the spectra of stars. A star's spectrum is the breakdown of its light into different colors. By analyzing the pattern of colors, scientists learn what elements are present within the star.

They found out that stars at 30KPC (kiloparsec) (100,000 light years) from the galactic center has the same metal content as stars found at the disk. Although this data for our galaxy disk has been revised, scientists still believe that our galaxy contains roughly 400 billion stars with countless planets, dust, comets and other objects. 

Source: Space.com https://www.space.com/41047-milky-way-galaxy-size-bigger-than-thought.html

THE MILKY WAY GALAXY IS NOW 2 MILLION LIGHT YEARS ACROSS

Astronomers have found the edge of the Milky Way at last

(Reposted, Source: ScienceNews.org) 

Our galaxy spans 1.9 million light-years, a new study finds

In this image from the Fermi space telescope, the Milky Way's stellar disk, which runs horizontally along the middle, glows in gamma rays. A vast halo of dark matter engulfs the disk and emits no light at all, which makes measuring the galaxy’s total size a challenge.

FERMI LAT COLLABORATION/DOE/NASA

Our galaxy is a whole lot bigger than it looks. New work finds that the Milky Way stretches nearly 2 million light-years across, more than 15 times wider than its luminous spiral disk. The number could lead to a better estimate of how massive the galaxy is and how many other galaxies orbit it.

Astronomers have long known that the brightest part of the Milky Way, the pancake-shaped disk of stars that houses the sun, is some 120,000 - 200,000 light-years across (SN: 8/1/19). Beyond this stellar disk is a disk of gas. A vast halo of dark matter, presumably full of invisible particles, engulfs both disks and stretches far beyond them (SN: 10/25/16). But because the dark halo emits no light, its diameter is hard to measure.

Now, Alis Deason, an astrophysicist at Durham University in England, and her colleagues have used nearby galaxies to locate the Milky Way’s edge. The precise diameter is 1.9 million light-years, give or take 0.4 million light-years, the team reports February 21 in a paper posted at arXiv.org.

To put that size into perspective, imagine a map in which the distance between the sun and the Earth is just one inch. If the Milky Way’s heart were at the center of the Earth, the galaxy’s edge would be four times farther away than the moon actually is.

To find the Milky Way’s edge, Deason’s team conducted computer simulations of how giant galaxies like the Milky Way form. In particular, the scientists sought cases where two giant galaxies arose side by side, like the Milky Way and Andromeda, our nearest giant neighbor, because each galaxy’s gravity tugs on the other (SN: 5/12/15). The simulations showed that just beyond the edge of a giant galaxy’s dark halo, the velocities of small nearby galaxies drop sharply (SN: 3/11/15).

Using existing telescope observations, Deason and her colleagues found a similar plunge in the speeds of small galaxies near the Milky Way. This occurred at a distance of about 950,000 light-years from the Milky Way’s center, marking the galaxy’s edge, the scientists say. The edge is 35 times farther from the galactic center than the sun is.

Although dark matter makes up most of the Milky Way’s mass, the simulations reveal that stars should also exist at these far-out distances. “Both have a well-defined edge,” Deason says. “The edge of the stars is very sharp, almost like the stars just stop at a particular radius.”

In the future, astronomers can refine the location of the Milky Way’s edge by discovering additional small galaxies nearby. Astronomers could also search for individual stars out at the boundary, says Mike Boylan-Kolchin, an astrophysicist at the University of Texas at Austin who was not involved with the study. The farthest such stars will be very dim, but future observations should be able to find them.

The measurement should also help astronomers tease out other galactic properties. For instance, the larger the Milky Way, the more massive it is — and the more galaxies there should be revolving around it, says Rosemary Wyse, an astronomer at Johns Hopkins University who was not part of the new work. So far, there are about 60 known Milky Way satellites, but astronomers suspect that many more await discovery.

Disclaimer: This is a repost from www.sciencenews.org