Posts tagged Milky Way
Posts tagged Milky Way
Structure and Evolution of Galaxies
As much as we know about galaxies, the evolution of galaxies is one of the mysteries of the Universe. By looking far out into space and equivalently, far back into time, astronomers can look at the oldest galaxies and make comparisons with modern-day galaxies to get a sense of how they’re evolving. To really understand galaxy evolution, though, one must understand the details of the structure of galaxies; therein lies many wondrous secrets of galaxies. We will focus on spiral galaxies:
The Structure of Spiral Galaxies
Most spiral galaxies have similar features, the most significant of which include a dark matter halo, the galactic disc, spiral arms, a central bulge (most containing a bar-like structure), and a stellar halo.
The dark matter halo is believed to be the main structural component of the Milky Way galaxy whose functional purpose is primarily to hold together the galaxy; without it, the galaxy would not be gravitationally bound. The dark matter halo is situated well beyond the visible galactic disc which is detected using observations like rotation curves of galaxies. Current observations suggest that dark matter accounts for roughly 95% of the Milky Way’s mass, while the other 5% is accounted for with normal, baryonic matter. It is currently believed that dark matter played a significant role in the evolution of galaxies, initiating clumps of matter in the early Universe which eventually lead to structures like galaxies.
The galactic disc is the location of most of the interstellar medium (ISM, composed of gas and dust) and also contains a substantial amount of stars which orbit in roughly circular orbits confined to the galactic plane; it consists of most of the visible matter in the galaxy. The Sun is located about 8.5kpc (kiloparsecs) from the galactic center in the galactic disc. The spiral arms within the galactic disc are the main sites of star formation; the blue spiral arms are indicators of young, hot stars. Within the galactic disc is where most cosmic recycling occurs and as a result, the ISM has a higher metallicity than primordial gas. The metallicity-age relation is important for understanding galaxy evolution. Most open clusters are found in the galactic disc, but some globular clusters (roughly one third) are found here, as well. Open clusters are very young because they are loosely bound and are easily disrupted. Open clusters have high metallicities because they are formed from more recently formed ISM which has had time to become enriched with metals. In contrast, globular clusters are very old as they are strongly gravitationally bound. Since globular clusters consist of the oldest stars in the galaxy, the metallicity-age relation suggests that they should have very low metallicities but those found in the galactic disc have unusually high metallicities; this suggests that cosmic recycling enriches the contents of the globular clusters.
The stellar halo extends further than the galactic disc itself and is roughly spherical in shape. Here lie roughly two thirds of the galaxy’s globular clusters. The globular clusters found here, as expected, have very low metallicities because they are young and do not get contaminated by the cosmic recycling that takes place in the galactic disc. The stellar halo’s star formation has long since ceased; there is very little ISM left in the stellar halo. The stars within the stellar halo have largely elliptical and highly irregular orbital motions which are not confined to the galactic plane.
What Does Any of This Tell Us About Galaxy Evolution?
Without the dark matter halo, our galaxy wouldn’t be gravitationally bound the way it is today. With this, along with the fact that dark matter consists of 95% of the galaxy’s mass, it is suggested that dark matter played a key role in the initial formation of galaxies. The spiral arms of the galaxy suggest that the galaxy is rotating, which is well supported by observations. Older stars contained in the stellar halo having irregular, elliptical orbits and younger stars confined in the galactic disc having regular, circularized orbits suggests that the galaxy started out in a disordered state which over time settled down to a more orderly state; the galaxy originated as a large gas cloud that eventually collapsed and through the conservation of angular momentum, became a flat, rotating disc. The fact that globular clusters within the galactic disc have unusually high metallicities suggest that cosmic recycling is the origin; as time progresses, high mass stars explode and contaminate the surrounding ISM to further enrich future stars’ chemical composition. Furthermore, globular clusters which were once believed to originate from the Milky Way are now believed to having been captured by the Sagittarius Dwarf galaxy, which suggests that even though the galactic halo is the oldest component of the galaxy, it is still a dynamic part of the Milky Way. Currently, the Milky Way is in a collision course with its neighbour, the Andromeda galaxy. In about 4 billion years, the two spiral galaxies will collide to form what astronomers like to call the Milkomeda galaxy.
Echinopsis Atacamensis and the Milky Way
The Light of Stars
What’s moving? Time lapse videos of the sky can be quite spectacular when they last long enough for stars, planets, aurora, and clouds to appear to move in just a few seconds. Pictured above, however, astrovideographer Daniel López not only treats us to several inspiring time lapse videos of the night sky, but shows us how he used sliders and motorized cranes to move the imaging cameras themselves, creating a thrilling three-dimensional sense of depth. The video sequences were taken from Tenerife on the Canary Islands of Spain over the past two months, and show scenes including sunset shadows approaching Observatorio del Teide, the Milky Way shifting as the sky rotates, bright planets Venus and trailing Jupiter setting, a reddened Moon rising through differing layers of atmospheric refraction, the MAGIC gamma-ray telescopes slewing to observe a new source, and unusual foreground objects including conic Echium wildpretii plants, unusual rock formations, and a spider moving about its web. The video concludes by showing the Belt of Venus descending on Mt. Teide as the morning sun rises.
This stunning photo of the Milky Way was captured from what may be the coldest and most isolated research facility on Earth: the French-Italian Concordia Base station, located at 3,200 meters (nearly 10,500 feet) altitude on the Antarctic plateau, 1,670 km (1,037 miles) from the geographic south pole.
Taken by Dr. Alexander Kumar, a doctor, researcher and photographer who’s been living at the Base since January, the image shows the full beauty of the sky above the southern continent — a sky that doesn’t see the Sun from May to August.
During the winter months no transportation can be made to or from Concordia Base — no deliveries or evacuations, not for any reason. The team there is truly alone, very much like future space explorers will one day be. This isolation is one reason that Concordia is used by ESA for research for missions to Mars.[Read More]
“This leaves us the rather discomforting conclusion that most of the inner part of the Galaxy including the Sun might not be saved from M31 after all, and the possibility of a merger in another 4 billion years cannot be ruled out.”
- Somak Raychaudhury and Donald Lynden-Bell
Monthly Notices of the Royal Astronomical Society 1989
The harsh reality of the distant universe with all of its violent interactions seems remote from our human existence and all might seem to be quiet and normal in our home the Milky Way. But it seems likely that in a mere 3 billion years, our neighbouring galaxy Andromeda and the Milky Way will fall together and have a close collision. They will likely merge and be reborn as a single giant elliptical galaxy over the course of another billion years or so. How might this metamorphosis play out and what might you see if you looked up at night over the next 4 billion years! The space between stars is so vast compared to their size that during a galaxy collision no individual stars actually collide with one another. So our sun and its family of planets will be taking a passive but exciting ride through the pair of coalescing galaxies and take on a spectacular view of the unfolding disaster in relative safety.
By exploiting a lucky accident, astronomers have for the first time measured a key property of a spiral galaxy located more than nine billion light-years away. The observations show that oxygen and iron abound at the centre of the galaxy but not at its edge, which suggests spiral galaxies – including Andromeda and our own Milky Way – formed their giant discs of stars from the inside out.
Spanning 120,000 light years, our galaxy’s disc outshines the rest of the Milky Way. The disc harbours the Sun and most of the galaxy’s other stars, as well as the beautiful spiral arms. But exactly how the disc formed is unknown.
One clue comes from the metallicity of the disc’s constituent stars. Metallicity is a measure of the relative abundance in a star of elements other than hydrogen and helium. Stars create these elements and spew them into space. Because stars congregate at a galaxy’s centre, the metallicity in most nearby spirals is greatest there and drops toward the edge. In the Milky Way’s disc, for example, travel 10,000 light-years outward and the metallicity falls 35%.
Baja California Timelapses
by Mike Flores
By now you may have heard the report that as many as 1/4 of all the sun-like stars in the Milky Way may have Earth-like worlds. Briefly, astronomers studied 166 stars within 80 light years of Earth, and did a survey of the planets they found orbiting them. What they found is that about 1.5% of the stars have Jupiter-mass planets, 6% have Neptune-mass ones, and about 12% have planets from 3 – 10 times the Earth’s mass.
This sample isn’t complete, and they cannot detect planets smaller than 3 times the Earth’s mass. But using some statistics, they can estimate from the trend that as many as 25% of sun-like stars have earth-mass planets orbiting them!
The universe hates you. Let’s get that out of the way right now. The universe loathes your guts and is infuriated by the way you dress, and the stupid way you talk sends it into a murderous rage. It’s just one bad morning and an empty coffee canister away from driving to your house and shanking you in the neck. With a supernova. It may happen tomorrow, or it may take billions of years. The universe is patient. It can wait. But rest assured: Some day, when you least expect it, it will reap a terrible vengeance from you. And it will go a little something like this:
Explanation: Is this what will become of our Milky Way Galaxy? Perhaps if we collide with the Andromeda Galaxy in a few billion years, it might. Pictured above is NGC 7252, a jumble of stars created by a huge collision between two large galaxies. The collision will take hundreds of millions of years and so is effectively caught frozen in time in the above image. The resulting pandemonium has been dubbed the Atoms-for-Peace galaxy because of its similarity to a cartoon of a large atom. The above image was taken recently by the MPG/ESO 2.2 meter telescope in Chile. NGC 7252 spans about 600,000 light years and lies about 220 million light years away toward the constellation of the Water Bearer (Aquarius). Since the sideways velocity of the Andromeda Galaxy (M31) is presently unknown, no one really knows for sure if the Milky Way will ever collide with M31.