How Big Is The Milky Way?

Wednesday, January 21, 2015

How Big Is The Milky Way?

The summertime Milky Way from Scorpius to Cygnus is broader and brighter than the winter version because we look into the direction of its center. Credit: Stephen Bockhold

The Milky Way is our home galaxy, the spot where the Earth resides. We are not anywhere near the center — NASA says we’re roughly 165 quadrillion miles from the galaxy’s black hole, for example — which demonstrates just how darn big the galaxy is. So how big is it, and how does it measure up with other neighborhood residents?

The numbers are pretty astounding. NASA estimates the galaxy at 100,000 light-years across. Since one light year is about 9.5 x 10¹²km, so the diameter of the Milky Way galaxy is about 9.5 x 10¹⁷ km in diameter. The thickness of the galaxy ranges depending on how close you are to the center, but it’s tens of thousands of light-years across.

Our galaxy is part of a collection known as the Local Group. Because some of these galaxies are prominent in our sky, the names tend to be familiar. The Milky Way is on a collision course with the most massive member of the group, called M31 or the Andromeda Galaxy. The Milky Way is the second-largest member, with M33 (the Triangulum Galaxy) the third-largest, NASA says. Andromeda appears much brighter in the night sky due to its size and relatively closer distance. There are about 30 members of this group.

The Andromeda Galaxy will collide with the Milky Way in the future. Credit: Adam Evans

Because we are inside the Milky Way’s arms, it appears as a band of stars (or a fuzzy white band) across the Earth’s sky. Casting a pair of binoculars or a telescope across it shows a mix of lighter areas and darker areas; the darker areas are dust that obscures any light from stars, galaxies and other bright objects behind it. From the outside, however, astronomers say the Milky Way is a barred spiral galaxy — a galaxy that has a band of stars across its center as well as the spiral shape.

If you’re looking for the center of the galaxy, gaze at the constellation Sagittarius, which is low on the summer sky horizon for most northern hemisphere residents. The constellation contains a massive radio source known as Sagittarius A*. Astronomers using the Chandra space telescope discovered why this supermassive black hole is relatively weak in X-rays: it’s because hot gas is being pulled inside the nebula, and most of it (99%) gets ejected and diffused.

Sagittarius A in infrared (red and yellow, from the Hubble Space Telescope) and X-ray (blue, from the Chandra space telescope). Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

Based on observing globular clusters (star clusters) in the galaxy, astronomers have estimated the Milky Way’s overall age at 13.5 billion years old — just two million years younger than the rest of the universe.

However, scientists are beginning to think that different parts of the galaxy formed at different times. In 2012, for example, astronomers led by Jason Kalirai of the Space Telescope Science Institute pinned down the age of the Milky Way’s inner halo of stars: 11.5 billion years old. They used white dwarfs, the burned-out remnants of Sun-like stars, to make that measurement.

Kalirai’s group’s research indicates that the Milky Way formed in the following sequence: the halo (including globular star clusters and dwarf galaxies), the inner halo (whose stars were born as a result of this construction) and the outer halo (created when the Milky Way ate up nearby ancient dwarf galaxies).

Artist’s impression of the structure of the Milky Way’s halo. Credit: NASA, ESA, and A. Feild (STScI)

While we’ve been focusing on the parts of the galaxy that you can see, in reality most of its mass is made up of dark matter. NASA estimates that there is about 10 times the mass of dark matter than the visible matter in the universe. (Dark matter is a form of matter that we cannot sense with conventional telescopic instruments, except through its gravitational effect on other things such as galaxies. When masses gather in high enough concentrations, they can bend the light of other objects.)

We have written many articles about the Milky Way for Universe Today. Here’s an article about the rotation of Milky Way, and here are some facts about the Milky Way. We’ve also recorded an episode of Astronomy Cast about galaxies. Listen here, Episode 97: Galaxies.

About Elizabeth Howell

Elizabeth Howell is the senior writer at Universe Today. She also works for Space.com, Space Exploration Network, the NASA Lunar Science Institute, NASA Astrobiology Magazine and LiveScience, among others. Career highlights include watching three shuttle launches, and going on a two-week simulated Mars expedition in rural Utah. You can follow her on Twitter @howellspace or contact her at her website.

FASHION WEEK - USA Fashion and Music News
GOOGLE NEWS - Google News Blogger
PINTEREST ACROSS THE UNIVERSE - Google Images Nasa Images
LAST FM - Download Music Legally Direct From Artist
WOMEN COMMUNITY - Women Communty Photography Videos Beauty
DISNEY CHANNEL - Photos and Music News
BABY JUSTIN BIEBER - Google Images Google News
LADY GAGA - Google Images Google News
ACROSS THE UNIVERSE - Google Images Universe Pictures
VICTORIA´S SECRET COMMUNITY - Victoria´s Secret Fashion Show Photos

No comments:

Post a Comment

NASA Photos Photography

The National Aeronautics and Space Administration (NASA) is the United States government agency responsible for the civilian space program as well as aeronautics and aerospace research. President Dwight D. Eisenhower established the National Aeronautics and Space Administration (NASA) in 1958 with a distinctly civilian (rather than military) orientation encouraging peaceful applications in space science. The National Aeronautics and Space Act was passed on July 29, 1958, disestablishing NASA's predecessor, the National Advisory Committee for Aeronautics (NACA). The new agency became operational on October 1, 1958.

UFO SIGHTINGS PHOTO PHOTOGRAPHY

The Oxford English Dictionary defines a UFO as "An unidentified flying object; a 'flying saucer'." The first published book to use the word was authored by Donald E. Keyhoe. The acronym "UFO" was coined by Captain Edward J. Ruppelt, who headed Project Blue Book, then the USAF's official investigation of UFOs. He wrote, "Obviously the term 'flying saucer' is misleading when applied to objects of every conceivable shape and performance. For this reason the military prefers the more general, if less colorful, name: unidentified flying objects. UFO (pronounced Yoo-foe) for short." Other phrases that were used officially and that predate the UFO acronym include "flying flapjack", "flying disc", "unexplained flying discs", "unidentifiable object", and "flying saucer". The phrase "flying saucer" had gained widespread attention after the summer of 1947. On June 24, a civilian pilot named Kenneth Arnold reported seeing nine objects flying in formation near Mount Rainier. Arnold timed the sighting and estimated the speed of discs to be over 1,200 mph (1,931 km/h). At the time, he described the objects' shape as being somewhat disc-like or saucer-like, leading to newspaper accounts of "flying saucers" and "flying discs". In popular usage the term UFO came to be used to refer to claims of alien spacecraft. and because of the public and media ridicule associated with the topic, some investigators prefer to use such terms as unidentified aerial phenomenon (or UAP) or anomalous phenomena, as in the title of the National Aviation Reporting Center on Anomalous Phenomena (NARCAP).

UFO PHOTO PHOTOGRAPHY

UFO - Unidentified Flying Object An unidentified flying object, or UFO, in its most general definition, is any apparent anomaly in the sky that is not identifiable as a known object or phenomenon. Culturally, UFOs are associated with claims of visitation by extraterrestrial life or government-related conspiracy theories, and have become popular subjects in fiction. While UFOs are often later identified, sometimes identification may not be possible owing to the usually low quality of evidence related to UFO sightings (generally anecdotal evidence and eyewitness accounts). Stories of fantastical celestial apparitions have been told since antiquity, but the term "UFO" (or "UFOB") was officially created in 1953 by the United States Air Force (USAF) to serve as a catch-all for all such reports. In its initial definition, the USAF stated that a "UFOB" was "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." Accordingly, the term was initially restricted to that fraction of cases which remained unidentified after investigation, as the USAF was interested in potential national security reasons and/or "technical aspects" (see Air Force Regulation 200-2). During the late 1940s and through the 1950s, UFOs were often referred to popularly as "flying saucers" or "flying discs". The term UFO became more widespread during the 1950s, at first in technical literature, but later in popular use. UFOs garnered considerable interest during the Cold War, an era associated with a heightened concern for national security. Various studies have concluded that the phenomenon does not represent a threat to national security nor does it contain anything worthy of scientific pursuit (e.g., 1951 Flying Saucer Working Party, 1953 CIA Robertson Panel, USAF Project Blue Book, Condon Committee).

Photos of Nature | Nature Photography What is The Universe

Photos of Nature | Nature Photography What is The Universe

Wednesday, January 21, 2015