Ask Ethan: If Gravity Attracts, How Can The ‘Dipole Repeller’ Push The Milky Way? (Synopsis) [Starts With A Bang]

“For the first time, astronomers have outlined and named the network of galaxies that includes the Milky Way, adding a line to our cosmic address and further defining our place in the universe.” -Douglas Quenqua

There’s been a longstanding puzzle in astrophysics that’s finally coming to a head. For nearly a century, we’ve known that our Universe is expanding, and that the distance to a galaxy determines its average apparent recessional speed from us. But on top of that is an additional motion — a peculiar velocity — caused by the local gravitational field of the Universe.

A two-dimensional slice of the overdense (red) and underdense (blue/black) regions of the Universe nearby us. Image credit: Cosmic Flows Project/University of Hawaii, via http://ift.tt/zGFsoA.

When we look at the motion of our own galaxy, we see it’s moving about twice as fast in one direction as the attractive masses would allow. But underdense regions, where there’s less mass and gravity than average, can serve as an effective repeller, failing to attract other matter just as much as overdense regions can attract it. Thanks to a newly mapped and accounted for cosmic void, we might finally understand how our galaxy is moving through the Universe.

Dipoles are most common in electromagnetism, where we think of negative as attractive and positive as repulsive. If you thought of this gravitationally, negative would be ‘extra mass’ and therefore attractive, while positive would be ‘less mass’ and therefore, relative to everything else, repulsive. Image credit: Wikimedia Commons user Maschen.

The so-called Great Attractor has nothing on the dipole repeller idea, and at long last the Milky Way’s motion might be understood!

from ScienceBlogs http://ift.tt/2jLn20k

“For the first time, astronomers have outlined and named the network of galaxies that includes the Milky Way, adding a line to our cosmic address and further defining our place in the universe.” -Douglas Quenqua

There’s been a longstanding puzzle in astrophysics that’s finally coming to a head. For nearly a century, we’ve known that our Universe is expanding, and that the distance to a galaxy determines its average apparent recessional speed from us. But on top of that is an additional motion — a peculiar velocity — caused by the local gravitational field of the Universe.

A two-dimensional slice of the overdense (red) and underdense (blue/black) regions of the Universe nearby us. Image credit: Cosmic Flows Project/University of Hawaii, via http://ift.tt/zGFsoA.

When we look at the motion of our own galaxy, we see it’s moving about twice as fast in one direction as the attractive masses would allow. But underdense regions, where there’s less mass and gravity than average, can serve as an effective repeller, failing to attract other matter just as much as overdense regions can attract it. Thanks to a newly mapped and accounted for cosmic void, we might finally understand how our galaxy is moving through the Universe.

Dipoles are most common in electromagnetism, where we think of negative as attractive and positive as repulsive. If you thought of this gravitationally, negative would be ‘extra mass’ and therefore attractive, while positive would be ‘less mass’ and therefore, relative to everything else, repulsive. Image credit: Wikimedia Commons user Maschen.

The so-called Great Attractor has nothing on the dipole repeller idea, and at long last the Milky Way’s motion might be understood!

from ScienceBlogs http://ift.tt/2jLn20k