Starburst Galaxies

Starburst Galaxies The universe is filled with galaxies, which are themselves filled with stars. At some point in its life, each galaxy bristled with star formation in vast clouds of hydrogen gas. Even today, some galaxies seem to have more than the usual amount of star birth activity and astronomers want to know why. There were so many stars being born in some galaxies in earlier times that they probably looked like cosmic fireworks bursts. Astronomers refer to these hotbeds of star birth as starburst galaxies. Key Takeaways: Starburst Galaxies Starburst galaxies are galaxies where high rates of star formation has occurred very quickly.Nearly all types of galaxies can undergo starburst events if conditions are right.Astronomers know that starburst galaxies are often involved in mergers that mingle stars and gas. Shock waves push the gas, which sets off the starburst activity. Starburst galaxies have unusually high  rates of star formation, and those bursts last for a short time during the galaxys long life. Thats because star formation burns through the gas reserves of the galaxy very quickly. It is likely that the sudden burst of star birth is triggered by a specific event. In most cases, a galaxy merger does the trick. Thats when two or more galaxies mesh together in a long gravitational dance and eventually meld together. During the merger, the gases of all the galaxies involved are mixed together. The collision sends shock waves through those gas clouds, which compress the gases and set off bursts of star formation.   Properties of Starburst Galaxies Starburst galaxies are not a  new type of galaxy, but rather simply a galaxy (or mingled galaxies) in a particular phase of their evolution. Even so, there are some properties that show up in most starburst galaxies: a very rapid star formation rate. These galaxies will produce stars at rates well above the average rate of most regular galaxies; availability of gas and dust. Some galaxies may have higher than normal star-formation rates simply due to their high volumes of gas and dust. However, some starburst galaxies do not a have the reserves to justify why they would have such high rates of star formation, so mergers may not be the only explanation;star formation rate is inconsistent with the age of the galaxy. The main point is that the current rate of star formation could not have been constant since the formation of the galaxy given its age. An older galaxy simply wouldnt have enough gas left over to keep up starbirth action for billions of years. In some starburst galaxies astronomers see a sudden burst of star birth, and often the explanation is a merger or chance encounter with another galaxy. Astronomers sometimes also compare the rate of star formation in a galaxy relative to its rotational period. If, for example, the galaxy exhausts all of its available gas during one rotation of the galaxy (given the high star formation rate), then it can be considered a starburst galaxy. The Milky Way rotates once every 220 million years; some galaxies go much slower, others faster. Another widely accepted method to see if a galaxy is a starburst is to compare the star formation rate against the age of the universe. If the current rate would exhaust all of the available gas in less time than 13.7 billion years, then its possible that a given galaxy may be in a starburst state.   Annotated image showing dazzling eyelid-like features bursting with stars in galaxy IC 2163. A tsunami of stars and gas triggered by a glancing collision with galaxy NGC 2207 (a portion of its spiral arm is shown on right side of image). ALMA image of carbon monoxide (orange), which revealed motion of the gas in these features, is shown on top of Hubble image (blue) of the galaxy. M. Kaufman; B. Saxton (NRAO/AUI/NSF); ALMA (ESO/NAOJ/NRAO); NASA/ESA Hubble Space Telescope Types of Starburst Galaxies Starburst activity can occur in galaxies ranging from spirals to irregulars. Astronomers who study these objects classify them into sub-types that help describe their ages and other characteristics. Starburst galaxy types include: Wolf-Rayet galaxies:  defined by their ratio of bright stars that fall into the Wolf-Rayet classification. Galaxies of this type have regions of high stellar wind, driven by the Wolf-Rayet stars. Those stellar monsters are incredibly massive and luminous and have very high rates of mass loss. The winds that they produce can collide with regions of gas and drive rapid star formation.Blue compact galaxies:  low mass galaxies that were once thought to be young galaxies, just beginning to form stars. However, they usually contain populations of very old stars. That usually is a good clue that the galaxy is quite old. Astronomers now suspect that blue compact galaxies are actually the result of mergers between galaxies of varying ages. Once they collide, starburst activity ramps up and lights up the galaxies.Luminous infrared galaxies:  dim, hidden galaxies that are difficult to study because they contain high levels of dust that can obscure observation. Typically infrared radiation   detected by telescopes is used to penetrate the dust. That provides clues to increased star formation. Some of these objects have been found to contain multiple supermassive black holes, which can shut down star formation. The increase in star birth in such galaxies has to be the result of a recent galaxy merger. Cause of Increased Star Formation Although the merger of galaxies is pinpointed as the main cause of star birth in these galaxies, the exact processes are not well understood. Partially, this is due to the fact that starburst galaxies come in many shapes and sizes, so there may be more than one condition that leads to increased star formation. However, for a starburst galaxy to even form, there must be lots of gas available to generate the new stars. Also, something must disturb the gas, to begin the gravitational collapse process that leads to the creation of new objects. Those two requirements led astronomers to suspect galaxy mergers and shock waves as two processes that can lead to starburst galaxies.   Centaurus A galaxy has a massive black hole at its heart that is actively gobbling up material. The actions of such active galactic nuclei may play a role in starbursts in galaxies.   ESO/WFI (Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); NASA/CXC/CfA/R.Kraft et al. (X-ray) Two other possibilities for the cause of starburst galaxies include: Active Galactic Nuclei (AGN): Virtually all galaxies contain a supermassive black hole in their core. Some galaxies appear to be in a state of high activity, where the central black hole is ejecting massive amounts of energy.  There is a great deal of evidence to show that the presence of such a black hole can dampen star formation activity. However, in the case of these so-called active  galactic nuclei, they can also, under the right conditions, trigger rapid star formation as the accretion of matter in a disk and its eventual ejection away from the black hole can create shockwaves that could trigger star formation.High supernova rates: Supernovae are violent events. If the rate of explosions increases due to the presence of a very high number of aging stars in a compact area, the resulting shockwaves can begin a rapid increase in star formation. However, this such an event to occur the conditions would have to be ideal; more so than in the other possibilities listed here. A supernova can push clouds of nearby gas around spur limited amounts of starbirth. This supernova is shown in a Hubble Space Telescope view of the Crab Nebula supernova remnant. NASA/ESA/STScI Starburst galaxies remain an active area of investigation by astronomers. The more they find, the better scientists can describe the actual conditions that lead up to the bright bursts of star formation that populate these galaxies.   Edited and updated by Carolyn Collins Petersen.

Important Cover Letter Trends in 2017 That Will Help Your Job Search

Important Cover Letter Trends in 2017 That Will Help Your Job Search One must never underestimate the importance of a good cover letter. Once you’ve got your resume in shape, this should be your main focus in job searching. A good cover letter can get you through a door that your resume couldn’t. So sit down, and start writing to impress. You probably already know the basics:Keep your letter to one page. Remember, you only have about 10 seconds to get HR’s attention.Give them a sense of who you are, first and foremost, both as a person and a candidate.Encourage readers to consult your resume- so they’ll see that the skills listed in the job post match yours. And remember not to focus too much on your duties, but on selling yourself as a candidate.Write a brand new letter for every single application.Get your reader’s attention in the first two sentences. Include as many keywords as you can cram in reasonably and convincingly; this lets them know that you are hip to the lingo of the job and of the industry.Use the ter minology when you can. Repeat the exact job description language wherever possible.In addition to the usual tricks, there are several trends every year in what’s in or out in the world of cover letters. Here are some things to keep in mind for 2017:1. Body copy is the new cover letter.If you’re submitting through an online site, remember that if your resume gets auto-screened and dumped, your cover letter will get dumped right along with it. Do everything you can to send your job materials to a hiring manager directly via email. That way you can use your cover letter as the body text of your email, and ensure it will be read.2. Include contact info.Sometimes it is possible to get hired without a resume. If this is the case, remember to always include your contact information in a footer- in your email or your cover letter itself. That way a hiring manager can always get in touch with you.3. Be specific.Keep in mind exactly who you are addressing your letter to and addr ess it to them by name. Also be very clear on the position you are applying for, and make sure your letter reflects this specificity. One candidate. One letter. One job.4. Check it twice.Tolerance for spelling and grammar mistakes is on the wane. Make spell check and a good grammarian friend your ally. If you want your letter read, write it well. And keep it clean and mistake free.5. Don’t just regurgitate your resume.Make it new and fresh and really sell your candidacy to this particular decision-maker for this particular job.6. Focus outward.Too much personalization can be a bad thing. Remember to go through and edit for too many â€Å"I† statements. Put the focus a little bit more on them, not on you. It’ll be obvious who is writing the letter; you don’t need to hammer that one home. They know who you are and that you want them to hire you. Concentrate instead on how you are ideally suited to helping the company meet their needs and goals. Show how you r skills and experience are valuable to them. Put their needs first.7. Be clear.Err on the side of clarity. Don’t try to get too cute or fancy. Follow all the rules above and make sure you’re still clearly and effectively communicating the requisite information, and you should be in good shape for a successful job search in the new year.