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margarita2007
margarita2007

... accreted earlier than surviving one • Surviving satellites are predominantly low-mass systems and have been accreted recently • The building blocks of the stellar halo were on average more massive and were accreted (and disrupted) earlier than de population of satellites that survive until the prese ...
ptolemy day 21 - Arts of Liberty
ptolemy day 21 - Arts of Liberty

Chapter 18 The Bizarre Stellar Graveyard What is a white dwarf
Chapter 18 The Bizarre Stellar Graveyard What is a white dwarf

... • What would it be like to visit a black hole? – You can orbit a black hole like any other object of the same mass—black holes don’t ...
Core-collapse supernovae and their massive progenitors
Core-collapse supernovae and their massive progenitors

Measuring the Milky Way
Measuring the Milky Way

... These objects are very close to the Galactic center. The orbit on the right is the best fit; it assumes a central black hole of 3.7 million solar masses. ...
Comprehensive Census and Complete Characterization of Nearby
Comprehensive Census and Complete Characterization of Nearby

... stars (Høg et al. 2000) as a compatible match given the reliable optical photometry and proper motions. Lacking accurate Hipparcos parallax measurements, we used the total proper motion (μtot ) as a proxy for distance and selected sources with μtot > 25 mas yr−1 corresponding to within 200 pc. These ...
PDF only - at www.arxiv.org.
PDF only - at www.arxiv.org.

Lecture 15 Star Formation and Evolution 3/7
Lecture 15 Star Formation and Evolution 3/7

... • test out model of stellar evolution using Star Clusters • HR diagram of a cluster gives “snapshot” of stars with the same age but different masses • Birth  Main Sequence  Red Giant  “live+die” faster if higher mass • tell age of cluster by most massive star still on Main Sequence ...
AST4930 Star and Planet Formation
AST4930 Star and Planet Formation

... the actual fraction of stars in multiple systems, its variation with stellar mass (e.g., massive stars more likely to be in multiple systems than low-mass stars), and the companion mass distribution. “stellar IMF” – corrected for multiplicity “system IMF” – uncorrected ...
Modeling the Photophoretic Force and Brownian Motion of a Single
Modeling the Photophoretic Force and Brownian Motion of a Single

... process, where solid material in a protoplanetary disk grows from micrometer sized dust grains to kilometer sized objects. One force which could be important is the photophoretic force. Dust grains illuminated by the central star will be unevenly heated. As gas molecules come into contact with the w ...
The Milky Way Galaxy (ch. 23)
The Milky Way Galaxy (ch. 23)

... nearly spherical shape, rest of gas collapsed to disk which has formed stars continuously since that time. (Think about how above properties suggest this.) More recently it was discovered that our Galaxy has a weak but detectable bar structure in the bulge. This rotating bar is important, because it ...
Neutron Star
Neutron Star

Chapter 23 The Milky Way Galaxy
Chapter 23 The Milky Way Galaxy

1e 1048.1−5937, xte j1810−197 and 4u 0142+61
1e 1048.1−5937, xte j1810−197 and 4u 0142+61

9 Dwarf Galaxies
9 Dwarf Galaxies

Chapter 4 Galactic Chemical Evolution
Chapter 4 Galactic Chemical Evolution

... The material we find around us in the Universe today contains significant quantities of heavy elements, although these are still only minor contributors to the total mass of baryonic matter (most is hydrogen). These heavy elements have been synthesised in nuclear reactions in stars, a process known ...
PH607lec10-4gal2
PH607lec10-4gal2

... Best interpretation of many of these is a trend in star formation history  Early type spirals formed most of their stars early on (used up their gas, have older/redder stars)  Late type spirals have substantial on-going star-formation, didn’t form as many stars early-on (and thus lots of gas left) ...
The Life Cycle of Stars
The Life Cycle of Stars

... helium into carbon (like our Sun). The core of a massive star becomes so hot that when helium is no longer available for fusion, carbon undergoes fusion. This produces heavier elements, beginning with oxygen and up to iron. Once iron is produced in the core, fusion can no longer occur. (This is beca ...
Nebula
Nebula

... seen as dark clouds in front of more distant stars or in front of emission nebulae. ...
Spiral galaxies: Spiral galaxies: Inclination Spiral galaxies: Internal
Spiral galaxies: Spiral galaxies: Inclination Spiral galaxies: Internal

Age aspects of habitability - Cambridge University Press
Age aspects of habitability - Cambridge University Press

... collisions between asteroids, planetesimals or even possible planets (Song et al. 2005). Out of these seven stars, five are young systems within their first Gyr of life. It is also well-known that solar-type stars remain very active in the first billion years of their life, sustaining conditions tha ...
Word doc - GDN - University of Gloucestershire
Word doc - GDN - University of Gloucestershire

... One of the predictions of the Big Bang model for the origin of the Universe is that the initial explosion was extremely hot and that the remnants of the initial fireball might still be detected at the edges of the Universe. Support for this hypothesis came from the discovery in the 1960s by Arno Pen ...
Sun, Moon, Earth,
Sun, Moon, Earth,

No Slide Title
No Slide Title

Main Sequence Lifetime
Main Sequence Lifetime

... • Stars in this phase have a narrow range of luminosities, about one hundredth of their luminosity at the time of the helium flash, but still much more luminous than their main sequence ...
< 1 ... 28 29 30 31 32 33 34 35 36 ... 158 >

Nebular hypothesis

The nebular hypothesis is the most widely accepted model in the field of cosmogony to explain the formation and evolution of the Solar System. It suggests that the Solar System formed from nebulous material. The theory was developed by Immanuel Kant and published in his Universal Natural History and Theory of the Heaven. Originally applied to our own Solar System, this process of planetary system formation is now thought to be at work throughout the universe. The widely accepted modern variant of the nebular hypothesis is the solar nebular disk model (SNDM) or simply solar nebular model. This nebular hypothesis offered explanations for a variety of properties of the Solar System, including the nearly circular and coplanar orbits of the planets, and their motion in the same direction as the Sun's rotation. Some elements of the nebular hypothesis are echoed in modern theories of planetary formation, but most elements have been superseded.According to the nebular hypothesis, stars form in massive and dense clouds of molecular hydrogen—giant molecular clouds (GMC). These clouds are gravitationally unstable, and matter coalesces within them to smaller denser clumps, which then rotate, collapse, and form stars. Star formation is a complex process, which always produces a gaseous protoplanetary disk around the young star. This may give birth to planets in certain circumstances, which are not well known. Thus the formation of planetary systems is thought to be a natural result of star formation. A Sun-like star usually takes approximately 1 million years to form, with the protoplanetary disk evolving into a planetary system over the next 10-100 million years.The protoplanetary disk is an accretion disk that feeds the central star. Initially very hot, the disk later cools in what is known as the T tauri star stage; here, formation of small dust grains made of rocks and ice is possible. The grains eventually may coagulate into kilometer-sized planetesimals. If the disk is massive enough, the runaway accretions begin, resulting in the rapid—100,000 to 300,000 years—formation of Moon- to Mars-sized planetary embryos. Near the star, the planetary embryos go through a stage of violent mergers, producing a few terrestrial planets. The last stage takes approximately 100 million to a billion years.The formation of giant planets is a more complicated process. It is thought to occur beyond the so-called frost line, where planetary embryos mainly are made of various types of ice. As a result, they are several times more massive than in the inner part of the protoplanetary disk. What follows after the embryo formation is not completely clear. Some embryos appear to continue to grow and eventually reach 5–10 Earth masses—the threshold value, which is necessary to begin accretion of the hydrogen–helium gas from the disk. The accumulation of gas by the core is initially a slow process, which continues for several million years, but after the forming protoplanet reaches about 30 Earth masses (M⊕) it accelerates and proceeds in a runaway manner. Jupiter- and Saturn-like planets are thought to accumulate the bulk of their mass during only 10,000 years. The accretion stops when the gas is exhausted. The formed planets can migrate over long distances during or after their formation. Ice giants such as Uranus and Neptune are thought to be failed cores, which formed too late when the disk had almost disappeared.
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