Featured Research

from universities, journals, and other organizations

Figure eights and peanut shells: How stars move at the center of the galaxy

Date:
November 27, 2013
Source:
Royal Astronomical Society (RAS)
Summary:
Two months ago astronomers created a new 3-D map of stars at the center of our Galaxy (the Milky Way), showing more clearly than ever the bulge at its core. Previous explanations suggested that the stars that form the bulge are in banana-like orbits, but a new article suggests that the stars probably move in peanut-shell or figure of eight-shaped orbits instead.

An artist’s impression showing how the Milky Way galaxy would look seen from almost edge on and from a very different perspective than we get from the Earth. The central bulge shows up as a peanut shaped glowing ball of stars and the spiral arms and their associated dust clouds form a narrow band.
Credit: ESO/NASA/JPL-Caltech/M./Kornmesser/R. Hurt

Two months ago astronomers created a new 3D map of stars at the centre of our Galaxy (the Milky Way), showing more clearly than ever the bulge at its core. Previous explanations suggested that the stars that form the bulge are in banana-like orbits, but a paper published this week in Monthly Notices of the Royal Astronomical Society suggests that the stars probably move in peanut-shell or figure of eight-shaped orbits instead.

Related Articles


The difference is important; astronomers develop theories of star motions to not only understand how the stars in our galaxy are moving today but also how our galaxy formed and evolves. The Milky Way is shaped like a spiral, with a region of stars at the centre known as the "bar," because of its shape. In the middle of this region, there is a "bulge" that expands out vertically.

In the new work Alice Quillen, professor of astronomy at the University of Rochester, and her collaborators created a mathematical model of what might be happening at the centre of the Milky Way. Unlike the Solar System where most of the gravitational pull comes from the Sun and is simple to model, it is much harder to describe the gravitational field near the centre of the Galaxy, where millions of stars, vast clouds of dust, and even dark matter swirl about. In this case, Quillen and her colleagues considered the forces acting on the stars in or near the bulge.

As the stars go round in their orbits, they also move above or below the plane of the bar. When stars cross the plane they get a little push, like a child on a swing. At the resonance point, which is a point a certain distance from the centre of the bar, the timing of the pushes on the stars is such that this effect is strong enough to make the stars at this point move up higher above the plane. (It is like when a child on the swing has been pushed a little every time and eventually is swinging higher.) These stars are pushed out from the edge of the bulge.

The resonance at this point means that stars undergo two vertical oscillations for every orbital period. But what is the most likely shape of the orbits in between? The researchers showed through computer simulations that peanut-shell shaped orbits are consistent with the effect of this resonance and could give rise to the observed shape of the bulge, which is also like a peanut-shell.

Next month the European Space Agency will launch the Gaia spacecraft, which is designed to create a 3D map of the stars in the Milky Way and their motions. This 3D map will help astronomers better understand the composition, formation and evolution of our Galaxy.

"It is hard to look back into the past of our galaxy and know what was there, but simulations can give us clues," explained Quillen. "Using my model I saw that, over time, the resonance with the bar, which is what leads to these peculiarly shaped orbits, moves outwards. This may be what happened in our Galaxy."

"Gaia will generate huge amounts of data -- on billions of stars," said Quillen. This data will allow Quillen and her colleagues to finesse their model further. "This can lead to a better understanding of how the Milky Way might have evolved into the shape it has today."

Quillen explained that there are different models as to how the galactic bulge was formed. Astronomers are interested in finding out how much the bar has slowed down over time and whether the bulge "puffed up all at once or slowly." Understanding the distributions of speeds and directions of motion (velocities) of the stars in the bar and the bulge might help determine this evolution.

"One of the predictions of my model is that there is a sharp difference in the velocity distributions inside and outside the resonance," Quillen said. "Inside -- closer to the galactic centre -- the disk should be puffed up and the stars there would have higher vertical velocities. Gaia will measure the motions of the stars and allow us to look for variations in velocity distributions such as these."

To be able to generate a model for the orbits of stars in the bulge, Quillen needed to factor in different variables. She first needed to understand what happens at the region of the resonance, which depends on the speed of the rotating bar and the mass density of the bar.

"Before I could model the orbits, I needed the answer to what I thought was a simple question: what is the distribution of material in the inner galaxy?" Quillen said. "But this wasn't something I could just look up. Luckily my collaborator Sanjib Sharma was able to help out."

Sharma worked out how the speed of circular orbits changed with distance from the galactic centre (called the rotation curve). Using this information, Quillen could compute a mass density at the location of the resonance, which she needed for her model.

Quillen was also able to combine the new orbit models with the speed of the bar (which is rotating) to get a more refined estimate of the mass density 3000 light years from the Galaxy centre (about one eighth of the distance from the centre of the Galaxy to Earth), which is where the edge of the bulge is.

And there is not long now to wait now for Gaia to start collecting data. Gaia's launch time is set for 0912 GMT on December 19, and will be streamed live on the ESA Portal.


Story Source:

The above story is based on materials provided by Royal Astronomical Society (RAS). Note: Materials may be edited for content and length.


Journal Reference:

  1. Alice C. Quillen, Ivan Minchev, Sanjib Sharma, Yu-Jing Qin, Paola Di Matteo. A Vertical Resonance Heating Model for X- or Peanut-Shaped Galactic Bulges. Monthly Notices of the Royal Astronomical Society, 2013 [link]

Cite This Page:

Royal Astronomical Society (RAS). "Figure eights and peanut shells: How stars move at the center of the galaxy." ScienceDaily. ScienceDaily, 27 November 2013. <www.sciencedaily.com/releases/2013/11/131127110309.htm>.
Royal Astronomical Society (RAS). (2013, November 27). Figure eights and peanut shells: How stars move at the center of the galaxy. ScienceDaily. Retrieved November 21, 2014 from www.sciencedaily.com/releases/2013/11/131127110309.htm
Royal Astronomical Society (RAS). "Figure eights and peanut shells: How stars move at the center of the galaxy." ScienceDaily. www.sciencedaily.com/releases/2013/11/131127110309.htm (accessed November 21, 2014).

Share This


More From ScienceDaily



More Space & Time News

Friday, November 21, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Crowdfunded Moon Mission Offers To Store Your Digital Memory

Crowdfunded Moon Mission Offers To Store Your Digital Memory

Newsy (Nov. 19, 2014) Lunar Mission One is offering to send your digital memory (or even your DNA) to the moon to be stored for a billion years. Video provided by Newsy
Powered by NewsLook.com
Accidents Ignite Debate on US Commercial Space Travel

Accidents Ignite Debate on US Commercial Space Travel

AFP (Nov. 19, 2014) Serious accidents with two US commercial spacecraft within a week of each-other in October have re-ignited the debate over the place of private corporations in the exploration of space. Duration: 02:08 Video provided by AFP
Powered by NewsLook.com
Lunar Mission One Could Send Your Hair to The Moon

Lunar Mission One Could Send Your Hair to The Moon

Buzz60 (Nov. 19, 2014) A British-led venture called Lunar Mission One plans to send a module to the moon with keepsakes from Earth. Vanessa Freeman (@VanessaFreeTV) tells you how to get your photos and DNA onboard. Video provided by Buzz60
Powered by NewsLook.com
Why A Russian Object Is Being Called A 'Satellite Killer'

Why A Russian Object Is Being Called A 'Satellite Killer'

Newsy (Nov. 18, 2014) An unidentified Russian spacecraft is getting some attention, with some saying it could be for research while others say it could be a weapon. Video provided by Newsy
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:

Strange & Offbeat Stories


Space & Time

Matter & Energy

Computers & Math

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile: iPhone Android Web
Follow: Facebook Twitter Google+
Subscribe: RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins