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From B.tech students , Presidency University:

Created & Designed by:

Prakhar Mishra

UNIVERSE FOR US:

In the recent Scenario , the universe has experienced a wild variety of changes resulting in mass temperature change of planets , stars as well as other celestial bodies , with the recent abandoned massive explosion , the super karnet galaxy was destroyed over 8 million planets and other celestial objects from its super nova explosion which resulted in massive distortion of other moving objects in universe and also disturbed the galaxy astronomy , scientists believe the way the universe is evolving , the universe is going to build the obscure impact of nature in the recent 2 million years which is going to have devastating effects in nature ….see our recent posts for more info:.

The universe square theory:

The earliest cosmological models of the Universe were developed by ancient Greek and Indian philosophers and were geocentric, placing Earth at the center.^[13]^[14] Over the centuries, more precise astronomical observations led Nicolaus Copernicus to develop the heliocentric model with the Sun at the center of the Solar System. In developing the law of universal gravitation, Isaac Newton built upon Copernicus’ work as well as Johannes Kepler‘s laws of planetary motion and observations by Tycho Brahe.

Further observational improvements led to the realization that the Sun is one of hundreds of billions of stars in the Milky Way, which is one of at least hundreds of billions of galaxies in the Universe. Many of the stars in our galaxy have planets. At the largest scale, galaxies are distributed uniformly and the same in all directions, meaning that the Universe has neither an edge nor a center. At smaller scales, galaxies are distributed in clusters and superclusters which form immense filaments and voids in space, creating a vast foam-like structure.

How Old is the Universe?

Age may only be a number, but when it comes to the age of the universe, it’s a pretty important one. According to research, the universe is approximately 13.8 billion years old. How did scientists determine how many candles to put on the universe’s birthday cake? They can determine the age of the universe using two different methods: by studying the oldest objects within the universe and measuring how fast it is expanding.

Age limits

The universe cannot be younger than the objects contained inside of it. By determining the ages of the oldest stars, scientists are able to put a limit on the age.

The life cycle of a star is based on its mass. More massive stars burn faster than their lower-mass siblings. A star 10 times as massive as the sun will burn through its fuel supply in 20 million years, while a star with half the sun’s mass will last more than 20 billion years. The mass also affects the brightness, or luminosity, of a star; more massive stars are brighter. [Related: The Brightest Stars: Luminosity & Magnitude]

Known as Population III stars, the first stars were massive and short-lived. They contained only hydrogen and helium, but through fusion began to create the elements that would help to build the next generation of stars. Scientists have been hunting for traces of the first stars for decades.

“Those stars were the ones that formed the first heavy atoms that ultimately allowed us to be here,” David Sobral, an astronomer from the University of Lisbon in Portugal, said in a statement. Sobral was part of a team that identified a bright galaxy with evidence of Population III stars.

“The detection of dust in the early universe provides new information on when the first supernovae exploded and hence the time when the first hot stars bathed the universe in light,” ESO officials said in a statement. “Determining the timing of this ‘cosmic dawn’ is one of the holy grails of modern astronomy, and it can be indirectly probed through the study of early interstellar dust.”

Early stars aren’t the only way to place limits on the age of the universe. Dense collections of stars known as globular clusters have similar characteristics. The oldest known globular clusters have stars with ages that appear to be between 11 and 14 billion years old. The wide range comes from problems in pinpointing the distances to the clusters, which affects estimates of brightness and thus mass. If the cluster is farther away than scientists have measured, the stars would be brighter, thus more massive, thus younger than calculated.

“Just like archaeologists use fossils to reconstruct the history of the Earth, astronomers use globular clusters to reconstruct the history of the galaxy,” Andrea Kunder told Space.com. “There are only about 150 globular clusters known in the Milky Way Galaxy, so each of these globular clusters is an important tracer of the galactic halo and the formation of the Milky Way Galaxy.”

The uncertainty still creates a limit to the age of the universe; it must be at least 11 billion years old. It can be older, but not younger.

Expansion of the universe

The universe we live in is not flat and unchanging, but constantly expanding. If the expansion rate is known, scientists can work backwards to determine the universe’s age, much like police officers can unravel the initial conditions that resulted in a traffic accident. Thus, finding the expansion rate of the universe — a number known as the Hubble constant — is key.

A number of factors determine the value of this constant. The first is the type of matter that dominates the universe. Scientists must determine the proportion of regular and dark matter to dark energy. Density also plays a role. A universe with a low density of matter is older than a matter-dominated one.

To determine the density and composition of the universe, scientists rely on missions such as NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) and The European Space Agency’s Planck spacecraft. By measuring the thermal radiation left over from the Big Bang, missions such as these are able to determine the density, composition and expansion rate of the universe. The leftover radiation is known as the cosmic microwave background, and both WMAP and Planck have mapped it. [INFOGRAPHIC: Cosmic Microwave Background: Big Bang Relic Explained]

In 2012, WMAP estimated the age of the universe to be 13.772 billion years, with an uncertainty of 59 million years. In 2013, Planck measured the age of the universe at 13.82 billion years. Both of these fall within the lower limit of 11 billion years independently derived from the globular clusters, and both have smaller uncertainties than that number.

NASA’s Spitzer Space Telescope has also contributed to narrowing down the age of the universe by reducing the uncertainty of the Hubble constant. Combined with the WMAP measurements, scientists were able to make independent calculations of the pull of dark energy.

“Just over a decade ago, using the words ‘precision’ and ‘cosmology’ in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two,” Wendy Freedman of the Observatories of the Carnegie Institution for Science in Pasadena, California, said in a statement. Freedman lead the study that used Spitzer to refine the Hubble constant. “Now we are talking about accuracies of a few percent. It is quite extraordinary.”

Editor’s Note: This article was updated on Jan. 8, 2019 to reflect a correction. The original article stated that the oldest stars have been estimated to be up to 18 billion years old.

A White Dwarf’s Giant Planet

on DECEMBER 6, 2019

Calling it a ‘chance discovery,’ the University of Warwick’s Boris Gänsicke recently presented the results of his team’s study of some 7,000 white dwarf stars, all of them cataloged by the Sloan Digital Sky Survey. One drew particular interest because chemical elements turned up in spectroscopic studies indicating something unusual. Says Gänsicke, “We knew that there had to be something exceptional going on in this system, and speculated that it may be related to some type of planetary remnant.”

And that makes the star WDJ0914+1914 an example of what a stellar system that survived, at least partially, the red giant phase of its host star might look like as a planet orbits the Earth-sized white dwarf. This work, which draws on data from the European Southern Observatory’s X-shooter spectrograph at the Very Large Telescope in Chile, confirms hydrogen, oxygen and sulphur associated with the white dwarf, all found in a disk of gas around the star rather than being present in the white dwarf itself. Subsequent work determined that the only way to produce this particular disk configuration was through evaporation of a giant planet.

Image: Artist’s impression of the WDJ0914+1914 system. Credit: ESO.

Thus this white dwarf makes history as the site of the first detection of a surviving giant planet around this class of star. You’ll recall previous work on white dwarf atmospheres, which has given us a look at the composition of infalling material that may have been the result of the breakup of a planet, comet or asteroid (see, for example, Survivors: White Dwarf Planets).

But now we’re looking at an actual planet in the act of shedding material while still retaining its structure. The oxygen, hydrogen and sulphur found here are similar to what we see in the deeper atmospheric layers of Neptune and Uranus. Placing such a planet in a tight orbit around a white dwarf would cause high levels of ultraviolet radiation to strip away the outer atmospheric layers, creating the same kind of disk we find at WD J0914+1914.

The star’s temperature is estimated at 28,000° Celsius, while the planet is at least twice as large as the star it orbits, a world whose atmosphere is being depleted due to interactions with the star’s high energy photons. While most of the gas escapes, about 3,000 tonnes per second fall onto the disk, which is what makes the presence of the planet accessible to observers.

Image: Location of WDJ0914+1914 in the constellation of Cancer. Credit: ESO.

The planet orbits the primary at a scant 15 times the stellar radius, meaning it is 10 million kilometers away from the star, in a place that would have once been deep inside the red giant that was the white dwarf’s progenitor. The assumption here is that the planet moved closer to the star after the white dwarf had formed, perhaps through gravitational interactions with other worlds in this system. We also get a glimpse of this system’s future in the paper:

Gravitational interactions in multi-planet systems can perturb planets onto orbits with peri-centres close to the white dwarf, where tidal effects are likely to lead to circularisation of the orbit. Common envelope evolution provides an alternative scenario to bring a planet into a close orbit around the white dwarf, though it requires rather fine-tuned initial conditions and only works for planets more massive than Jupiter… As the white dwarf continues to cool, the mass loss rate will gradually decrease, and become undetectable in ~ 350 Myr… By then, the giant planet will have lost ∼ 0.002 Jupiter masses (or ∼ 0.04 Neptune masses), i.e. an insignificant fraction of its total mass.

The paper also notes a possible analogue to WD J0914+1914 in HAT-P-26b, a Neptune-mass planet orbiting a K-class star with a period of 4.26 days, adding that despite its high temperature, the small radius of WD J0914+1914 would make its planet cooler than the equivalent around a main sequence star. As to how common such planets may be, of the 7,000 white dwarfs examined by this study, only one planet has emerged. The authors point out that we can look forward to studying the roughly 260,000 white dwarfs identified by the Gaia mission, and thus could well find in this larger sample enough planets to make comparative study possible.

The paper is Gänsicke et al., “Accretion of a giant planet onto a white dwarf star,” Nature 576 (2019), 61-64 (abstract / preprint).

CharterIn Centauri Dreams, Paul Gilster looks at peer-reviewed research on deep space exploration, with an eye toward interstellar possibilities. For the last twelve years, this site coordinated its efforts with the Tau Zero Foundation. It now serves as an independent forum for deep space news and ideas. In the logo above, the leftmost star is Alpha Centauri, a triple system closer than any other star, and a primary target for early interstellar probes. To its right is Beta Centauri (not a part of the Alpha Centauri system), with Beta, Gamma, Delta and Epsilon Crucis, stars in the Southern Cross, visible at the far right (image: Marco Lorenzi).

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