Two surveys of near-infrared light, which is sensitive primarily to red giants and not affected by dust extinction, detected the predicted overabundance in the Scutum–Centaurus arm but not in the Carina–Sagittarius arm: the Scutum–Centaurus Arm contains approximately 30% more red giants than would be expected in the absence of a spiral arm. Articles from Britannica Encyclopedias for elementary and high school students. Similarly, with the discovery of the Canis Major Dwarf Galaxy, it was found that a ring of galactic debris from its interaction with the Milky Way encircles the Galactic disk. [159], The apex of the Sun's way, or the solar apex, is the direction that the Sun travels through space in the Milky Way. [144] However, a few globular clusters have been found farther, such as PAL 4 and AM1 at more than 200,000 light-years from the Galactic Center. [181], In November 2018, astronomers reported the discovery of one of the oldest stars in the universe. These include Carina Dwarf, Draco Dwarf, and Leo II Dwarf. Launch into other worlds while testing your knowledge about space, celestial bodies, and the solar system. All the stars we see in the night sky are in our own Milky Way Galaxy. Here Are 300 Million, Maybe - A new analysis of data from NASA's Kepler spacecraft increases the number of habitable exoplanets thought to exist in this galaxy", "Release 15-001 – NASA's Chandra Detects Record-Breaking Outburst from Milky Way's Black Hole", Interpretation of velocity distribution of the inner regions of the Galaxy, Models for the inner regions of the Galaxy. The present interstellar gas contains elements heavier than helium at a level of about 2 percent by mass, while the globular clusters contain as little as 0.02 percent of the same elements. All of this adds up to give us a picture of the Milky Way, even though we can't get outside to see the whole thing. These stars form a large disk whose diameter is about 100,000 light years. (Credit: Credit: Urquhart JS, et al. Astronomers have identified some 700 young stars in this 2.5-light-year-wide area. In some it was possible to view massive star clusters still in the process of formation. This illustrates the fact that there are far more faint stars than bright stars: in the entire sky, there are about 500 stars brighter than apparent magnitude 4 but 15.5 million stars brighter than apparent magnitude 14. They are among the oldest stars formed in the Milky Way region. Relative to the celestial equator, it passes as far north as the constellation of Cassiopeia and as far south as the constellation of Crux, indicating the high inclination of Earth's equatorial plane and the plane of the ecliptic, relative to the galactic plane. [169] Nonetheless, these stars and clusters now comprise the stellar halo of the Milky Way. [185] This estimate was made using the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure the relative strengths of spectral lines caused by the presence of thorium and other elements created by the R-process. Theoretical models of clusters show how this effect changes the stellar content with time, and direct comparisons with real clusters give reliable ages for them. There has been some debate over the years as to whether the Milky Way has two spiral arms or four. The Milky Way is the second-largest galaxy in the Local Group (after the Andromeda Galaxy), with its stellar disk approximately 170,000–200,000 light-years (52–61 kpc) in diameter and, on average, approximately 1,000 ly (0.3 kpc) thick. 172, No. They are areas where very massive stars have recently formed, and many contain the uncondensed gas, dust, and molecular complexes commonly associated with ongoing star formation. Thus, to compare the Milky Way to the Hubble flow, one must consider a volume large enough so that the expansion of the Universe dominates over local, random motions. [137][138], A simulation published in 2011 suggested that the Milky Way may have obtained its spiral arm structure as a result of repeated collisions with the Sagittarius Dwarf Elliptical Galaxy. [84] The nearest exoplanet may be 4.2 light-years away, orbiting the red dwarf Proxima Centauri, according to a 2016 study. [34][186], According to observations utilizing adaptive optics to correct for Earth's atmospheric distortion, stars in the galaxy's bulge date to about 12.8 billion years old. The orbital speed of the Solar System about the center of the Milky Way is approximately 220 km/s (490,000 mph) or 0.073% of the speed of light. About 13.5 billion-years-old, 2MASS J18082002-5104378 B is a tiny ultra metal-poor (UMP) star made almost entirely of materials released from the Big Bang, and is possibly one of the first stars. [29][30] The dark matter halo around the Milky Way may span as much as 2 million light years. Our nearest large neighbor galaxy is the Andromeda galaxy. The Ancient Greek γαλαξίας (galaxias) – from root γαλακτ-, γάλα ("milk") + -ίας (forming adjectives) – is also the root of "galaxy", the name for our, and later all such, collections of stars. Measured ages of open clusters agree with the conclusions that have been reached about their life expectancies. “I was fascinated by the idea of planning this image; having the Milky Way arch above the ancient and lonely bell tower. Only three galaxies outside our own Milky Way Galaxy can be seen without a telescope, and appear as fuzzy patches in the sky with the naked eye. They have also detected over 150 protoplanetary disks, or proplyds, which are believed to be embryonic solar systems that will eventually form planets. [133][134][135] Thus, the Milky Way appears to have two spiral arms as traced by old stars and four spiral arms as traced by gas and young stars. The final list of members should contain only a very few nonmembers—either those that appear to agree with the group motion because of observational errors or those that happen to share the group’s motion at the present time but are not related to the group historically. The large-scale distribution of these clusters cannot be learned directly because their existence in the Milky Way plane means that dust obscures those that are more than a few thousand light-years from the Sun. The Sun is near the inner rim of the Orion Arm, within the Local Fluff of the Local Bubble, and in the Gould Belt. This was shot last October on a two-week photo tour with friends through the Southwest. Preliminary evidence indicates that the ratio of the abundance of the heavier elements among the detected gases to hydrogen decreases outward from the centre of the Galaxy, a tendency that has been observed in other spiral galaxies.