Category: universo

These dense, dark pillars of dust and gas ar…

These dense, dark pillars of dust and gas are resisting erosion from intense ultraviolet light released by the Orion Nebula’s biggest stars.
And new stars are forming. 

Credit: ESA/Hubble & NASA

A small portion of the rough-and-tumble neig…

A small portion of the rough-and-tumble neighborhood of swirling dust and gas near one of the most massive and eruptive stars in our galaxy is seen in this NASA/ESA Hubble Space Telescope image. This close-up view shows only a three light-year-wide portion of the entire Carina Nebula, which has a diameter of over 200 light-years. Located 8,000 light-years from Earth, the nebula can be seen in the southern sky with the naked eye. Credit: NASA/ESA, Hubble

Nearby dust clouds in the Milky Way Credi…

Nearby dust clouds in the Milky Way

Credit: NASA, ESA, and The Hubble Heritage Team (STScI/AURA)

The VISIR instrument on ESO’s VLT captured thi…

The VISIR instrument on ESO’s VLT captured this stunning image of a newly-discovered massive binary star system. Nicknamed Apep after an ancient Egyptian deity, it could be the first gamma-ray burst progenitor to be found in our galaxy.

Apep’s stellar winds have created the dust cloud surrounding the system, which consists of a binary star with a fainter companion. With 2 Wolf-Rayet stars orbiting each other in the binary, the serpentine swirls surrounding Apep are formed by the collision of two sets of powerful stellar winds, which create the spectacular dust plumes seen in the image.

The reddish pinwheel in this image is data from the VISIR instrument on ESO’s Very Large Telescope (VLT), and shows the spectacular plumes of dust surrounding Apep. The blue sources at the centre of the image are a triple star system — which consists of a binary star system and a companion single star bound together by gravity. Though only two star-like objects are visible in the image, the lower source is in fact an unresolved binary Wolf-Rayet star. The triple star system was captured by the NACOadaptive optics instrument on the VLT.

Credit: ESO/Callingham et al.

String Theory

String theory is a fascinating physical model in which all particles are replaced by one-dimensional objects known as strings. This theory says that we live in more than four dimensions, but we can not perceive them.

String theory, is a complete theory and unites quantum physics with Einstein’s general relativity.

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On distance scales larger than the string scale, a string looks just like an ordinary particle, with its mass, charge, and other properties determined by the vibrational state of the string. In string theory, one of the many vibrational states of the string corresponds to the graviton, a quantum mechanical particle that carries gravitational force. Thus string theory is a theory of quantum gravity.

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According to string theory, the reason we can not observe these dimensions is because they are very small and compact (smaller than the plank length 10 −35)

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Compactification is one way of modifying the number of dimensions in a physical theory. In compactification, some of the extra dimensions are assumed to “close up” on themselves to form circles. In the limit where these curled up dimensions become very small, one obtains a theory in which spacetime has effectively a lower number of dimensions. A standard analogy for this is to consider a multidimensional object such as a garden hose. If the hose is viewed from a sufficient distance, it appears to have only one dimension, its length. However, as one approaches the hose, one discovers that it contains a second dimension, its circumference. Thus, an ant crawling on the surface of the hose would move in two dimensions.

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Compactification can be used to construct models in which spacetime is effectively four-dimensional. However, not every way of compactifying the extra dimensions produces a model with the right properties to describe nature. In a viable model of particle physics, the compact extra dimensions must be shaped like a Calabi–Yau manifold

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Another approach to reducing the number of dimensions is the so-called brane-world scenario. In this approach, physicists assume that the observable universe is a four-dimensional subspace of a higher dimensional space. In such models, the force-carrying bosons of particle physics arise from open strings with endpoints attached to the four-dimensional subspace, while gravity arises from closed strings propagating through the larger ambient space. This idea plays an important role in attempts to develop models of real world physics based on string theory, and it provides a natural explanation for the weakness of gravity compared to the other fundamental forces

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One notable feature of string theories is that these theories require extra dimensions of spacetime for their mathematical consistency. In bosonic string theory, spacetime is 26-dimensional, while in superstring theory it is 10-dimensional, and in M-theory it is 11-dimensional. In order to describe real physical phenomena using string theory, one must therefore imagine scenarios in which these extra dimensions would not be observed in experiments.

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The original version of string theory was bosonic string theory, but this version described only bosons, a class of particles which transmit forces between the matter particles, or fermions. Bosonic string theory was eventually superseded by theories called superstring theories. These theories describe both bosons and fermions, and they incorporate a theoretical idea called supersymmetry.

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This is a mathematical relation that exists in certain physical theories between the bosons and fermions. In theories with supersymmetry, each boson has a counterpart which is a fermion, and vice versa.

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There are several versions of superstring theory: type I, type IIA, type IIB, and two flavors of heterotic string theory (SO(32) and E8×E8). The different theories allow different types of strings, and the particles that arise at low energies exhibit different symmetries. For example, the type I theory includes both open strings (which are segments with endpoints) and closed strings (which form closed loops), while types IIA, IIB and heterotic include only closed strings.

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Branes

In string theory and other related theories, a brane is a physical object that generalizes the notion of a point particle to higher dimensions. For instance, a point particle can be viewed as a brane of dimension zero, while a string can be viewed as a brane of dimension one. It is also possible to consider higher-dimensional branes. In dimension p, these are called p-branes. The word brane comes from the word “membrane” which refers to a two-dimensional brane

In string theory, D-branes are an important class of branes that arise when one considers open strings

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D-branes are typically classified by their spatial dimension, which is indicated by a number written after the D. A D0-brane is a single point, a D1-brane is a line (sometimes called a “D-string”), a D2-brane is a plane, and a D25-brane fills the highest-dimensional space considered in bosonic string theory. There are also instantonic D(–1)-branes, which are localized in both space and time.

Duality

A striking fact about string theory is that the different versions of the theory prove to be highly non-trivial in relation. One of the relationships that exist between different theories is called S-duality. This is a relationship that says that a collection of interacting particles in a theory may in some cases be viewed as a collection of weak interacting particles in a completely different theory. Approximately, a collection of particles is said to interact strongly if they combine and deteriorate frequently and interact poorly if they do so infrequently. The type I string theory turns out to be equivalent by S-duality to the heterotic string theory SO (32). Likewise, type IIB string theory is related to itself in a non-trivial way by S-duality

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Another relationship between different string theories is T-duality. Here one considers strings propagating around a circular extra dimension. T-duality states that a string propagating around a circle of radius R is equivalent to a string propagating around a circle of radius 1/R in the sense that all observable quantities in one description are identified with quantities in the dual description. For example, a string has momentum as it propagates around a circle, and it can also wind around the circle one or more times. The number of times the string winds around a circle is called the winding number. If a string has momentum p and winding number n in one description, it will have momentum n and winding number p in the dual description. For example, type IIA string theory is equivalent to type IIB string theory via T-duality, and the two versions of heterotic string theory are also related by T-duality.

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Black holes

In general relativity, a black hole is defined as a region of spacetime in which the gravitational field is so strong that no particle or radiation can escape. In the currently accepted models of stellar evolution, black holes are thought to arise when massive stars undergo gravitational collapse, and many galaxies are thought to contain supermassive black holes at their centers. 

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Black holes are also important for theoretical reasons, as they present profound challenges for theorists attempting to understand the quantum aspects of gravity. String theory has proved to be an important tool for investigating the theoretical properties of black holes because it provides a framework in which theorists can study their thermodynamics.

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The big bang theory doesn’t offer any explanation for what started the original expansion of the universe. This is a major theoretical question for cosmologists, and many are applying the concepts of string theory in attempts to answer it. One controversial conjecture is a cyclic universe model called the ekpyrotic universe theory, which suggests that our own universe is the result of branes colliding with each other.

Some things that string theory could explain: Neutrinos would have to have mass (minimum), Decay of Proton, New fields of force (short and long range) defined by some forms of calabi-yau, Explanations for Dark Matter.

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String theory is a very complex and broad area, so this post is only a summary. To better understand, I suggest you read Brian Greene’s books: The Elegant Universe and The Fabric of the Cosmo.

What’s happening around that star? An …

What’s happening around that star? An unusual spiral structure has been discovered around the Milky Way star R Sculptoris, a red giant star located about 1,500 light years away toward the constellation of the Sculptor (Sculptoris). The star was observed with the new Atacama Large Millimeter/submillimeter Array (ALMA), the most powerful telescopic array observing near millimeter wavelengths, that part of the spectrum situated well beyond red light but before microwaves and radio waves. Data from ALMA observations was used to create a 3D visualization of the gas and dust immediately surrounding the star. A digital slice through this data showed the unexpected spiral structure. Although unusual, a similar spiral pattern was discovered in visible light recently around LL Pegasi. Upon analyzing the data, a hypothesis was drawn that the red giant star in R Sculptoris might be puffing gas toward an unseen binary companion star. The dynamics of this system might be particularly insightful because it may be giving clues as to how giant stars evolve toward the end of their lives – and so release some constituent elements back to the interstellar medium so that new stars may form.

Visualization Credit: ALMA Observatory (ESO/NAOJ/NRAO)

An Alien Spacecraft May Have Passed Through Ou…

Slightly more than one year ago, we spotted an object from another star traveling through our Solar System for the first time. There was some debate over whether it was a comet or an asteroid – but could it instead have been an alien spacecraft equipped with a solar sail?

Well, no. But still, two scientists have looked into the plausibility of such a scenario anyway, noting some peculiarities in the object – dubbed ‘Oumuamua – that could lend credence to such an explanation. The story was first picked up by Matt Williams at Universe Today.

Oumuamua was odd in that, as it swung past the Sun, it appeared to get a strange speed boost. Scientists have put this down to an outgassing event – with the object firing material from its surface like a jet as it was heated by the Sun.

Bialy and Loeb, however, argue against such an idea. They say the lack of additional rotation in the 400-meter-long object (1,300 feet) caused by the event makes it unlikely an outgassing event was the cause of the change in motion. Instead, they say the acceleration “may be explained by solar radiation pressure”.

“If radiation pressure is the accelerating force, then ‘Oumuamua represents a new class of thin interstellar material, either produced naturally, through a yet unknown process in the ISM [interstellar medium] or in proto-planetary disks, or of an artificial origin,” they write.

“Considering an artificial origin, one possibility is that ‘Oumuamua is a lightsail, floating in interstellar space as a debris from an advanced technological equipment.”

Such ideas have been considered on Earth for our own journeys to distant stars. The Breakthrough Starshot project, for example, proposed using a lightsail to reach our nearest star system – Alpha Centauri – within a generation.

If this were true for ‘Oumumamua, the duo are unsure whether the object was accidentally sent towards us – “equipment that is not operational any more” – or an operational probe “sent intentionally to Earth vicinity by an alien civilization.” They say it could have come from any star within 16,000 light-years.

Unfortunately, ‘Oumuamua is now too far from Earth to study it further, let alone visit it, and it will never return again. So we’ll never be able to test this theory, however ridiculous it might be.

“The key issue with this theory is that it cannot possibly be tested,” Dr René Heller from the Max Planck Institute for Solar System Research told IFLScience. “It is also an extraordinary claim without extraordinary evidence.”

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ESO’s exquisitely sensitive GRAVITY instrument…

ESO’s exquisitely sensitive GRAVITY instrument has added further evidence to the long-standing assumption that a supermassive black hole lurks in the centre of the Milky Way. New observations show clumps of gas swirling around at about 30% of the speed of light on a circular orbit just outside a four million solar mass black hole — the first time material has been observed orbiting close to the point of no return, and the most detailed observations yet of material orbiting this close to a black hole.

This visualization uses data from simulations of orbital motions of gas swirling around at about 30% of the speed of light on a circular orbit around the supermassive black hole Sagittarius A*. 

This simulation shows the orbits of a tight group of stars close to the supermassive blackhole at the heart of the Milky Way. During 2018 one of these stars, S2, passed very close to the black hole and was the subject of intense scrutiny with ESO telescope. Its behaviour matched the predictions of Einsteins’s general relativity and was inconsistent with simpler Newtonian gravity.

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Spiral Galaxy NGC253 and Globular Cluster NG…

Spiral Galaxy NGC253 and Globular Cluster NGC288

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Eddie Trimarchi

Drake EquationWhat do we need to know about …

Drake Equation

What do we need to know about to discover life in space? How can we estimate the number of technological civilizations that might exist among the stars? While working as a radio astronomer at the National Radio Astronomy Observatory in Green Bank, West Virginia, Dr. Frank Drake conceived an approach to bound the terms involved in estimating the number of technological civilizations that may exist in our galaxy. The Drake Equation, as it has become known, was first presented by Drake in 1961 and identifies specific factors thought to play a role in the development of such civilizations. Although there is no unique solution to this equation, it is a generally accepted tool used by the scientific community to examine these factors.

  • N = The number of civilizations in the Milky Way Galaxy whose electromagnetic emissions are detectable.
  • R

    = The rate of formation of stars suitable for the development of intelligent life.

  • fp = The fraction of those stars with planetary systems.
  • ne = The number of planets, per solar system, with an environment suitable for life.
  • fl = The fraction of suitable planets on which life actually appears.
  • fi = The fraction of life bearing planets on which intelligent life emerges.
  • fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
  • L

    = The length of time such civilizations release detectable signals into space.

Original estimates

  • R = 1 yr−1 (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative)
  • fp = 0.2 to 0.5 (one fifth to one half of all stars formed will have planets)
  • ne = 1 to 5 (stars with planets will have between 1 and 5 planets capable of developing life)
  • fl = 1 (100% of these planets will develop life)
  • fi = 1 (100% of which will develop intelligent life)
  • fc = 0.1 to 0.2 (10–20% of which will be able to communicate)
  • L = 1000 to 100,000,000 years (which will last somewhere between 1000 and 100,000,000 years)

Within the limits of our existing technology, any practical search for distant intelligent life must necessarily be a search for some manifestation of a distant technology. In each of its last four decadal reviews, the National Research Council has emphasized the relevance and importance of searching for evidence of the electromagnetic signature of distant civilizations.

Besides illuminating the factors involved in such a search, the Drake Equation is a simple, effective tool for stimulating intellectual curiosity about the universe around us, for helping us to understand that life as we know it is the end product of a natural, cosmic evolution, and for making us realize how much we are a part of that universe. A key goal of the SETI Institute is to further high quality research that will yield additional information related to any of the factors of this fascinating equation. seti.org (read more)