A star is a massive, luminous ball of gas that is held together by its own gravity. The nearest star to Earth is the Sun. A star begins as a collapsing cloud of material composed primarily of hydrogen, along with helium and trace amounts of heavier elements. Once the stellar core is sufficiently dense, some of the hydrogen is steadily converted into helium through the process of nuclear fusion. For most of its life, a star shines due to thermonuclear fusion in its core releasing energy that traverses the star's interior and then radiates into space. Almost all elements heavier than hydrogen and helium were created by fusion processes in stars.

  • Galaxies Demand a Stellar Recount Featured News Article Galaxies Demand a Stellar Recount Galaxies Demand a Stellar Recount

    NASA JPL, Pasadena, CA (Aug. 20, 2009) – For decades, astronomers have gone about their business of studying the cosmos with the assumption that stars of certain sizes form in... More »

  • Massive Stars Near the Galactic Center Featured News Article Massive Stars Near the Galactic Center Massive Stars Near the Galactic Center

    Harvard-Smithsonian Center for Astrophysics (Sep. 12, 2009) – The Central Molecular Zone (CMZ) of our galaxy is a giant complex of molecular gas and dust situated in the... More »

  • Trifid Nebula: A Star Factory Featured News Article Trifid Nebula: A Star Factory Trifid Nebula: A Star Factory

    European Southern Observatory (Aug. 25, 2009) – Today ESO has released a new image of the Trifid Nebula, showing just why it is a firm favourite of astronomers, amateur and... More »

  • Formation of Stars in Young Clusters Featured News Article Formation of Stars in Young Clusters Formation of Stars in Young Clusters

    Harvard-Smithsonian Center for Astrophysics (Oct. 12, 2009) – Most stars form in clusters. Recent studies of nearby star forming regions find that about three-quarters of their... More »

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No Place to Hide: Missing Primitive Stars Outside Milky Way Uncovered Last Updated on 2010-02-19 16:09:05 GARCHING, GERMANY (Feb. 18, 2010) – After years of successful concealment, the most primitive stars outside our Milky Way galaxy have finally been unmasked. New observations using ESO’s Very Large Telescope have been used to solve an important astrophysical puzzle concerning the oldest stars in our galactic neighbourhood — which is crucial for our understanding of the earliest stars in the Universe. “We have, in effect, found a flaw in the forensic methods used until now,” says Else Starkenburg, lead author of the paper reporting the study. “Our improved approach allows us to uncover the primitive stars hidden among all the other, more common stars.” Primitive stars are thought to have formed from material forged shortly after the Big Bang, 13.7 billion years ago. They typically have less than one thousandth the amount of chemical elements... More »
First Stars Last Updated on 2009-11-11 16:17:31 New stars are continually forming in clouds of gas and dust in our galaxy. Astronomers at the CfA and elsewhere who watch these births have a very good (though not perfect) understanding of how and why they happen. The natal regions, however, are all rich in elements like carbon and oxygen whose properties facilitate the birth process. These elements, however, did not exist in the early universe - only hydrogen and helium (and a trace of some others) were made in the big bang processes of creation. All the other elements in our world were fabricated in the fusion furnaces of stars, and later ejected into space in supernovae or winds. How, then, did the very first generation of stars in the cosmos come to be without this facilitating material? Answering this fundamental question has long been a goal of astronomy, yet the first stars -- however they came to be -- must have existed so long... More »
Star Formation Last Updated on 2009-11-09 18:08:58 Stars form as gravitational forces coalesce the gas and dust in interstellar clouds until the material forms clumps dense enough to become stars. But how this happens, and whether or not the processes are the same for all stars remains very uncertain. Astronomers have been studying those clumps, the stellar wombs called "pre-stellar cores," in an attempt to sort out these questions. But precisely because the cores have no stars in them yet, or at best only very young stars, they are faint and difficult to study. SAO astronomers Erik Rosolowsky and Phil Myers, together with four of their colleagues, have completed the first unbiased census of 200 cores in three relatively nearby clouds of gas and dust. They combined observations from a millimeter wavelength study with their infrared images from the Spitzer Space telescope. The former observations are able to identify the... More »
Epsilon Eridani: a Young Solar System Last Updated on 2009-11-09 00:00:00 When the first infrared cosmic survey satellite, IRAS, looked at the nearby star Epsilon Eridani in 1984, it found that the star emitted a large excess of cool infrared radiation. This star is only 10.5 light-years from earth, and had already been carefully examined at optical wavelengths. Those studies had showed that it is quite similar to our sun in mass, but is much younger -- only about 850 million years old versus the sun's age of 4.5 billion years. When the sun was as young as Epsilon Eridani we think it was in the process of forming its system of planets. The discovery of strong excess infrared emission, therefore, immediately suggested that the star had a disk of preplanetary dust around it, and this dust was the source of the excess infrared. That conclusion has since been confirmed by other observations, and moreover other stars have been discovered with preplanetary,... More »
Double Jets in Young Binary Stars Last Updated on 2009-11-09 00:00:00 Most stars the size of the sun or larger (in mass) are part of multiple stellar systems in which two or even three stars orbit around one another. This tendency presumably reflects the conditions that existed when stars were born, since it is unlikely that stars pair up later on in their lives. The local conditions during star formation in turn reveal the complex environments when planets (if there are any) form around these stars. Binary stars might tend to disrupt the formation of any planets around them, for example. Star birth is typically accompanied by the production of narrow bipolar jets of gas that shoot out perpendicular to the (possibly protoplanetary) disks around the young stars. These jets of material provide important diagnostics of the young stars and their environments, and multiple stars should, it is thought, have multiple jets. But although multiplicity is common... More »