Galactic bar paradox resolved in cosmic dance

Date:
August 25, 2020
Source:
Royal Astronomical Society
Summary:
New light has been shed on a mysterious and long-standing conundrum
at the very heart of our galaxy. The new work offers a potential
solution to the so-called 'Galactic bar paradox', whereby different
observations produce contradictory estimates of the motion of the
central regions of the Milky Way.



FULL STORY ========================================================================== [Spiral galaxy concept | Credit: (c) Alexandr Mitiuc / stock.adobe.com]
Spiral galaxy concept illustration (stock image).

Credit: (c) Alexandr Mitiuc / stock.adobe.com [Spiral galaxy concept |
Credit: (c) Alexandr Mitiuc / stock.adobe.com] Spiral galaxy concept illustration (stock image).

Credit: (c) Alexandr Mitiuc / stock.adobe.com Close New light has
been shed on a mysterious and long-standing conundrum at the very
heart of our galaxy. The new work offers a potential solution to the
so-called 'Galactic bar paradox', whereby different observations produce contradictory estimates of the motion of the central regions of the
Milky Way. The results are published in Monthly Notices of the Royal Astronomical Society.


==========================================================================
The majority of spiral galaxies, like our home the Milky Way, host a large
bar- like structure of stars in their centre. Knowledge of the true bar
size and rotational speed is crucial for understanding how galaxies form
and evolve, as well as how they form similar bars throughout the Universe.

However our galaxy's bar size and rotational speed have been strongly
contested in the last 5 years; while studies of the motions of stars near
the Sun find a bar that is both fast and small, direct observations of
the Galactic central region agree on one that is significantly slower
and larger.

The new study, by an international team of scientists led by Tariq Hilmi
of the University of Surrey and Ivan Minchev of the Leibniz Institute
for Astrophysics Potsdam (AIP), suggests an insightful solution to this discrepancy. Analysing state-of-the-art galaxy formation simulations
of the Milky Way, they show that both the bar's size and its rotational
speed fluctuate rapidly in time, causing the bar to appear up to twice
as long and rotate 20 percent faster at certain times.

The bar pulsations result from its regular encounters with the Galactic
spiral arms, in what can be described as a "cosmic dance." As the bar and spiral arm approach each other, their mutual attraction due to gravity
makes the bar slow down and the spiral speed up. Once connected, the two structures move as one and the bar appears much longer and slower than
it actually is. As the dancers split apart, the bar speeds up while the
spiral slows back down.

"The controversy about the Galactic bar can then be simply resolved
if we happen to be living at a time when the bar and spiral are
connected, giving the illusion of a large and slow bar," comments Dr
Minchev. "However the motion of the stars near the Sun remains governed
by the bar's true, much smaller nature, and so those observations appear contradictory." Recent observations have confirmed that the inner Milky
Way spiral arm is currently connected to the bar, which happens about
once every 80 million years according to the simulations. Data from the forthcoming 3rd data release of the Gaia mission will be able to test
this model further, and future missions will discover if the dance goes
on in other galaxies across the Universe.


========================================================================== Story Source: Materials provided by Royal_Astronomical_Society. Note:
Content may be edited for style and length.


========================================================================== Related Multimedia:
* YouTube_video:_Simulation_of_the_Milky_Way's_bar_and_inner_spirals ========================================================================== Journal Reference:
1. T Hilmi, I Minchev, T Buck, M Martig, A C Quillen, G Monari,
B Famaey, R
S de Jong, C F P Laporte, J Read, J L Sanders, M Steinmetz, C Wegg.

Fluctuations in galactic bar parameters due to bar-spiral
interaction.

Monthly Notices of the Royal Astronomical Society, 2020; 497 (1):
933 DOI: 10.1093/mnras/staa1934 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/08/200825110723.htm

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