Astrophysics is a branch of space science that applies the laws of physics and chemistry to explain the birth, life and death of stars, planets, galaxies, nebulae and other objects in the universe. It has two sibling sciences, astronomy and cosmology, and the lines between them blur.

In the most rigid sense:

In practice, the three professions form a tight-knit family. Ask for the position of a nebula or what kind of light it emits, and the astronomer might answer first. Ask what the nebula is made of and how it formed and the astrophysicist will pipe up. Ask how the data fit with the formation of the universe, and the cosmologist would probably jump in. But watch out for any of these questions, two or three may start talking at once!

Astrophysicists seek to understand the universe and our place in it. At NASA, the goals of astrophysics are "to discover how the universe works, explore how it began and evolved, and search for life on planets around other stars," according NASA's website.

NASA states that those goals produce three broad questions:

While astronomy is one of the oldest sciences, theoretical astrophysics began with Isaac Newton. Prior to Newton, astronomers described the motions of heavenly bodies using complex mathematical models without a physical basis. Newton showed that a single theory simultaneously explains the orbits of moons and planets in space and the trajectory of a cannonball on Earth. This added to the body of evidence for the (then) startling conclusion that the heavens and Earth are subject to the same physical laws.

Perhaps what most completely separated Newton's model from previous ones is that it is predictive as well as descriptive. Based on aberrations in the orbit of Uranus, astronomers predicted the position of a new planet, which was then observed and named Neptune. Being predictive as well as descriptive is the sign of a mature science, and astrophysics is in this category.

Because the only way we interact with distant objects is by observing the radiation they emit, much of astrophysics has to do with deducing theories that explain the mechanisms that produce this radiation, and provide ideas for how to extract the most information from it. The first ideas about the nature of stars emerged in the mid-19th century from the blossoming science of spectral analysis, which means observing the specific frequencies of light that particular substances absorb and emit when heated. Spectral analysis remains essential to the triumvirate of space sciences, both guiding and testing new theories.

Early spectroscopy provided the first evidence that stars contain substances also present on Earth. Spectroscopy revealed that some nebulae are purely gaseous, while some contain stars. This later helped cement the idea that some nebulae were not nebulae at all they were other galaxies!

In the early 1920s, Cecilia Payne discovered, using spectroscopy, that stars are predominantly hydrogen (at least until their old age). The spectra of stars also allowed astrophysicists to determine the speed at which they move toward or away from Earth. Just like the sound a vehicle emits is different moving toward us or away from us, because of the Doppler shift, the spectra of stars will change in the same way. In the 1930s, by combining the Doppler shift and Einstein's theory of general relativity, Edwin Hubble provided solid evidence that the universe is expanding. This is also predicted by Einstein's theory, and together form the basis of the Big Bang Theory.

Also in the mid-19th century, the physicists Lord Kelvin (William Thomson) and Gustav Von Helmholtz speculated that gravitational collapse could power the sun, but eventually realized that energy produced this way would only last 100,000 years. Fifty years later, Einstein's famous E=mc2 equation gave astrophysicists the first clue to what the true source of energy might be (although it turns out that gravitational collapse does play an important role). As nuclear physics, quantum mechanics and particle physics grew in the first half of the 20th century, it became possible to formulate theories for how nuclear fusion could power stars. These theories describe how stars form, live and die, and successfully explain the observed distribution of types of stars, their spectra, luminosities, ages and other features.

Astrophysics is the physics of stars and other distant bodies in the universe, but it also hits close to home. According to the Big Bang Theory, the first stars were almost entirely hydrogen. The nuclear fusion process that energizes them smashes together hydrogen atoms to form the heavier element helium. In 1957, the husband-and-wife astronomer team of Geoffrey and Margaret Burbidge, along with physicists William Alfred Fowler and Fred Hoyle, showed how, as stars age, they produce heavier and heavier elements, which they pass on to later generations of stars in ever-greater quantities. It is only in the final stages of the lives of more recent stars that the elements making up the Earth, such as iron (32.1 percent), oxygen (30.1 percent), silicon (15.1 percent), are produced. Another of these elements is carbon, which together with oxygen, make up the bulk of the mass of all living things, including us. Thus, astrophysics tells us that, while we are not all stars, we are all stardust.

Becoming an astrophysicist requires years of observation, training and work. But you can start becoming involved in a small way even in elementary and high school, by joining astronomy clubs, attending local astronomy events, taking free online courses in astronomy and astrophysics, and keeping up with news in the field on a website such as Space.com.

In college, students should aim to (eventually) complete a doctorate in astrophysics, and then take on a post-doctoral position in astrophysics. Astrophysicists can work for the government, university labs and, occasionally, private organizations.

Study.com further recommends the following steps to put you on the path to being an astrophysicist:

Take math and science classes all through high school. Make sure to take a wide variety of science classes. Astronomy and astrophysics often blend elements of biology, chemistry and other sciences to better understand phenomena in the universe. Also keep an eye out for any summer jobs or internships in math or science. Even volunteer work can help bolster your resume.

Pursue a math- or science-related bachelor's degree. While a bachelor in astrophysics is the ideal, there are many other paths to that field. You can do undergraduate study in computer science, for example, which is important to help you analyze data. It's best to speak to your high school guidance counselor or local university to find out what degree programs will help you.

Take on research opportunities. Many universities have labs in which students participate in discoveries and sometimes even get published. Agencies such as NASA also offer internships from time to time.

Finish a doctorate in astrophysics. A Ph.D. is a long haul, but the U.S. Bureau of Labor Statistics points out that most astrophysicists do have a doctoral degree. Make sure to include courses in astronomy, computer science, mathematics, physics and statistics to have a wide base of knowledge.

Natalie Hinkel, a planetary astrophysicist who was then at Arizona State University, gave a lengthy interview with Lifehacker in 2015 that provided a glimpse into the rewards and challenges of being a junior astrophysics researcher. She described the long number of years she has put into doing her research, the frequent job switches, her work hours and what it's like to be a woman in a competitive field. She also had an interesting insight about what she actually did day to day. Very little of her time is spent at the telescope.

"I spend the vast majority of my time programming. Most people assume that astronomers spend all of their time at telescopes, but that's only a very small fraction of the job, if at all. I do some observations, but in the past few years I've only been observing twice for a total of about two weeks," Hinkel told Lifehacker.

"Once you get the data, you have to reduce it (i.e. take out the bad parts and process it for real information), usually combine it with other data in order to see the whole picture, and then write a paper about your findings. Since each observation run typically yields data from multiple stars, you don't need to spend all of your time at the telescope to have enough work."

Additional reporting by Elizabeth Howell, Space.com contributor.

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What is Astrophysics? | Space

In the Science Mission Directorate (SMD), the Astrophysics division studies the universe.The science goals of the SMD Astrophysics Division are breathtaking: we seek to understand the universe and our place in it. We are starting to investigate the very moment of creation of the universe and are close to learning the full history of stars and galaxies. We are discovering how planetary systems form and how environments hospitable for life develop. And we will search for the signature of life on other worlds, perhaps to learn that we are not alone.

NASA's goal in Astrophysics is to "Discover how the universe works, explore how it began and evolved, and search for life on planets around other stars." Three broad scientific questions emanate from these goals.

The National Academies have started work on the 2020 Decadal Survey on Astronomy and Astrophysics. Please visit the "2020 Decadal Planning" page for additional information about survey.

Astrophysics comprises of three focused and two cross-cutting programs. These focused programs provide an intellectual framework for advancing science and conducting strategic planning. They include:

The Astrophysics current missions include three of the Great Observatories originally planned in the 1980s and launched over the past 28 years. The current suite of operational Great Observatories include the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope. Additionally, the Fermi Gamma-ray Space Telescope explores the high-energy end of the spectrum. Innovative Explorer missions, such as the Neil Gehrels Swift Observatory, NuSTAR, TESS, as well as Mission of Opportunity NICER, complement the Astrophysics strategic missions. SOFIA, an airborne observatory for infrared astronomy, is in its operational phase. All of the missions together account for much of humanity's accumulated knowledge of the heavens. Many of these missions have achieved their prime science goals, but continue to produce spectacular results in their extended operations.

NASA-funded investigators also participate in observations, data analysis and developed instruments for the astrophysics missions of our international partners, including ESA's XMM-Newton.

The near future will be dominated by several missions. Currently in development, with especially broad scientific utility, is the James Webb Space Telescope. Also in work are detectors for ESA's Euclid mission and hardware for JAXA's XRISM (X-Ray Imaging and Spectroscopy) to provide breakthroughs in the study of structure formation of the universe, outflows from galaxy nuclei, and dark matter.

Completing the missions in development, supporting the operational missions, and funding the research and analysis programs will consume most of the Astrophysics Division resources.

In February 2016, NASA formally started the top Astro2010 decadal recommendation, the Wide Field Infrared Survey Telescope (WFIRST). WFIRST will aid researchers in their efforts to unravel the secrets of dark energy and dark matter, and explore the evolution of the cosmos. It will also discover new worlds outside our solar system and advance the search for worlds that could be suitable for life.

In January 2017, NASA selected the new Small Explorer (SMEX) mission IXPE (Imaging X-ray Polarimetry Explorer) which uses the polarization state of light from astrophysical sources to provide insight into our understanding of X-ray production in objects such as neutron stars and pulsar wind nebulae, as well as stellar and supermassive black holes.

In March 2017, NASA selected the Explorer Mission of Opportunity GUSTO (Galactic/Extragalactic ULDB Spectroscopic Terahertz Observatory) to measure emissions from the interstellar medium to help scientists determine the life cycle of interstellar gas in our Milky Way, witness the formation and destruction of star-forming clouds, and understand the dynamics and gas flow in the vicinity of the center of our galaxy.

Since the 2001 decadal survey, the way the universe is viewed has changed dramatically. More than 3800 planets have been discovered orbiting distant stars. Black holes are now known to be present at the center of most galaxies, including the Milky Way galaxy. The age, size and shape of the universe have been mapped based on the primordial radiation left by the big bang. And it has been learned that most of the matter in the universe is dark and invisible, and the universe is not only expanding, but accelerating in an unexpected way.

For the long term future, the Astrophysics goals will be guided based on the results of the 2010 Decadal survey New Worlds, New Horizons in Astronomy and Astrophysics. The priority science objectives chosen by the survey committee include: searching for the first stars, galaxies, and black holes; seeking nearby habitable planets; and advancing understanding of the fundamental physics of the universe.In 2016 the New Worlds, New Horizons: A Midterm Assessment was released.

In 2012 the Astrophysics Implementation Plan was released which describes the activities currently being undertaken in response to the decadal survey recommendations within the current budgetary constraints. The plan was updated in 2014, 2016, and most recently in 2018.

The Astrophysics roadmap Enduring Quests, Daring Visions was developed by a task force of the Astrophysics Subcommittee (APS) in 2013. The Roadmap presents a 30-year vision for astrophysics using the most recent decadal survey as the starting point.

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NASA Astrophysics | Science Mission Directorate

Branch of astronomy

Astrophysics is the branch of astronomy that employs the principles of physics and chemistry "to ascertain the nature of the astronomical objects, rather than their positions or motions in space".[1][2] Among the objects studied are the Sun, other stars, galaxies, extrasolar planets, the interstellar medium and the cosmic microwave background.[3][4] Emissions from these objects are examined across all parts of the electromagnetic spectrum, and the properties examined include luminosity, density, temperature, and chemical composition. Because astrophysics is a very broad subject, astrophysicists apply concepts and methods from many disciplines of physics, including classical mechanics, electromagnetism, statistical mechanics, thermodynamics, quantum mechanics, relativity, nuclear and particle physics, and atomic and molecular physics.

In practice, modern astronomical research often involves a substantial amount of work in the realms of theoretical and observational physics. Some areas of study for astrophysicists include their attempts to determine the properties of dark matter, dark energy, black holes, and other celestial bodies; whether or not time travel is possible, wormholes can form, or the multiverse exists; and the origin and ultimate fate of the universe.[3] Topics also studied by theoretical astrophysicists include Solar System formation and evolution; stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity, special relativity, quantum and physical cosmology, including string cosmology and astroparticle physics.

Astronomy is an ancient science, long separated from the study of terrestrial physics. In the Aristotelian worldview, bodies in the sky appeared to be unchanging spheres whose only motion was uniform motion in a circle, while the earthly world was the realm which underwent growth and decay and in which natural motion was in a straight line and ended when the moving object reached its destination. Consequently, it was held that the celestial region was made of a fundamentally different kind of matter from that found in the terrestrial sphere; either Fire as maintained by Plato, or Aether as maintained by Aristotle.[5][6]During the 17th century, natural philosophers such as Galileo,[7] Descartes,[8] and Newton[9] began to maintain that the celestial and terrestrial regions were made of similar kinds of material and were subject to the same natural laws.[10] Their challenge was that the tools had not yet been invented with which to prove these assertions.[11]

For much of the nineteenth century, astronomical research was focused on the routine work of measuring the positions and computing the motions of astronomical objects.[12][13] A new astronomy, soon to be called astrophysics, began to emerge when William Hyde Wollaston and Joseph von Fraunhofer independently discovered that, when decomposing the light from the Sun, a multitude of dark lines (regions where there was less or no light) were observed in the spectrum.[14] By 1860 the physicist, Gustav Kirchhoff, and the chemist, Robert Bunsen, had demonstrated that the dark lines in the solar spectrum corresponded to bright lines in the spectra of known gases, specific lines corresponding to unique chemical elements.[15] Kirchhoff deduced that the dark lines in the solar spectrum are caused by absorption by chemical elements in the Solar atmosphere.[16] In this way it was proved that the chemical elements found in the Sun and stars were also found on Earth.

Among those who extended the study of solar and stellar spectra was Norman Lockyer, who in 1868 detected radiant, as well as dark, lines in solar spectra. Working with chemist Edward Frankland to investigate the spectra of elements at various temperatures and pressures, he could not associate a yellow line in the solar spectrum with any known elements. He thus claimed the line represented a new element, which was called helium, after the Greek Helios, the Sun personified.[17][18]

In 1885, Edward C. Pickering undertook an ambitious program of stellar spectral classification at Harvard College Observatory, in which a team of woman computers, notably Williamina Fleming, Antonia Maury, and Annie Jump Cannon, classified the spectra recorded on photographic plates. By 1890, a catalog of over 10,000 stars had been prepared that grouped them into thirteen spectral types. Following Pickering's vision, by 1924 Cannon expanded the catalog to nine volumes and over a quarter of a million stars, developing the Harvard Classification Scheme which was accepted for worldwide use in 1922.[19]

In 1895, George Ellery Hale and James E. Keeler, along with a group of ten associate editors from Europe and the United States,[20] established The Astrophysical Journal: An International Review of Spectroscopy and Astronomical Physics.[21] It was intended that the journal would fill the gap between journals in astronomy and physics, providing a venue for publication of articles on astronomical applications of the spectroscope; on laboratory research closely allied to astronomical physics, including wavelength determinations of metallic and gaseous spectra and experiments on radiation and absorption; on theories of the Sun, Moon, planets, comets, meteors, and nebulae; and on instrumentation for telescopes and laboratories.[20]

Around 1920, following the discovery of the HertzsprungRussell diagram still used as the basis for classifying stars and their evolution, Arthur Eddington anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars.[22][23] At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = mc2. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even that stars are largely composed of hydrogen (see metallicity), had not yet been discovered.[non-primary source needed]

In 1925 Cecilia Helena Payne (later Cecilia Payne-Gaposchkin) wrote an influential doctoral dissertation at Radcliffe College, in which she applied ionization theory to stellar atmospheres to relate the spectral classes to the temperature of stars.[24] Most significantly, she discovered that hydrogen and helium were the principal components of stars. Despite Eddington's suggestion, this discovery was so unexpected that her dissertation readers convinced her to modify the conclusion before publication. However, later research confirmed her discovery.[25]

By the end of the 20th century, studies of astronomical spectra had expanded to cover wavelengths extending from radio waves through optical, x-ray, and gamma wavelengths.[26] In the 21st century it further expanded to include observations based on gravitational waves.

Observational astronomy is a division of the astronomical science that is concerned with recording and interpreting data, in contrast with theoretical astrophysics, which is mainly concerned with finding out the measurable implications of physical models. It is the practice of observing celestial objects by using telescopes and other astronomical apparatus.

The majority of astrophysical observations are made using the electromagnetic spectrum.

Other than electromagnetic radiation, few things may be observed from the Earth that originate from great distances. A few gravitational wave observatories have been constructed, but gravitational waves are extremely difficult to detect. Neutrino observatories have also been built, primarily to study our Sun. Cosmic rays consisting of very high energy particles can be observed hitting the Earth's atmosphere.

Observations can also vary in their time scale. Most optical observations take minutes to hours, so phenomena that change faster than this cannot readily be observed. However, historical data on some objects is available, spanning centuries or millennia. On the other hand, radio observations may look at events on a millisecond timescale (millisecond pulsars) or combine years of data (pulsar deceleration studies). The information obtained from these different timescales is very different.

The study of our very own Sun has a special place in observational astrophysics. Due to the tremendous distance of all other stars, the Sun can be observed in a kind of detail unparalleled by any other star. Our understanding of our own Sun serves as a guide to our understanding of other stars.

The topic of how stars change, or stellar evolution, is often modeled by placing the varieties of star types in their respective positions on the HertzsprungRussell diagram, which can be viewed as representing the state of a stellar object, from birth to destruction.

Theoretical astrophysicists use a wide variety of tools which include analytical models (for example, polytropes to approximate the behaviors of a star) and computational numerical simulations. Each has some advantages. Analytical models of a process are generally better for giving insight into the heart of what is going on. Numerical models can reveal the existence of phenomena and effects that would otherwise not be seen.[27][28]

Theorists in astrophysics endeavor to create theoretical models and figure out the observational consequences of those models. This helps allow observers to look for data that can refute a model or help in choosing between several alternate or conflicting models.

Theorists also try to generate or modify models to take into account new data. In the case of an inconsistency, the general tendency is to try to make minimal modifications to the model to fit the data. In some cases, a large amount of inconsistent data over time may lead to total abandonment of a model.

Topics studied by theoretical astrophysicists include stellar dynamics and evolution; galaxy formation and evolution; magnetohydrodynamics; large-scale structure of matter in the universe; origin of cosmic rays; general relativity and physical cosmology, including string cosmology and astroparticle physics. Astrophysical relativity serves as a tool to gauge the properties of large scale structures for which gravitation plays a significant role in physical phenomena investigated and as the basis for black hole (astro)physics and the study of gravitational waves.

Some widely accepted and studied theories and models in astrophysics, now included in the Lambda-CDM model, are the Big Bang, cosmic inflation, dark matter, dark energy and fundamental theories of physics. Wormholes are examples of hypotheses which are yet to be proven (or disproven).

The roots of astrophysics can be found in the seventeenth century emergence of a unified physics, in which the same laws applied to the celestial and terrestrial realms.[10] There were scientists who were qualified in both physics and astronomy who laid the firm foundation for the current science of astrophysics. In modern times, students continue to be drawn to astrophysics due to its popularization by the Royal Astronomical Society and notable educators such as prominent professors Lawrence Krauss, Subrahmanyan Chandrasekhar, Stephen Hawking, Hubert Reeves, Carl Sagan, Neil deGrasse Tyson and Patrick Moore. The efforts of the early, late, and present scientists continue to attract young people to study the history and science of astrophysics.[29][30][31]

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Astrophysics - Wikipedia

Astro-Physics products can be shipped to overseas destinations except for the following countries: Australia, France, Germany, Italy and Japan.

Astro-Physics is dedicated to the production and development of amateur telescopes and accessories. They strive to produce the highest possible quality telescope components at an affordable price. Astro-Physics builds optics, critical gears, circuit boards, and components including the knobs and fitting from scratch.

Astro-Physics offers a variety of telescope mounts andmount accessories, tube rings and photo / visual accessories.

The German Equatorial mounts Astro-Physics manufactures are: the Mach1GTO, 1100GTO, 1600GTOand 3600GTO. The Mach1GTO is compact, light-weight and portable. The 1100GTO German Equatorial Mount incorporates the design features of the 1600GTO in a smaller, more portable package.The 1600GTO can be used for basic configuration or with the optional Absolute Encoders it can go into demanding astro-imaging. The 3600GTO is the solution for imaging with large instruments or with a combined weight.

Mounting plates are another product of Astro-Physics. They produce an arrangement of dovetail mountings and fixed mountings. Astro-Physics also offer an array of accessories from counterweight shaft options, shaft extension and shaft safety parts, tripod, piers, power supplies and so much more. From the smallest accessory to the largest telescope mount you will find Astro-Physics products to be of the finest quality.

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Astro-Physics - Buy Telescopes

Deep in the thick, poisonous clouds wrapped around Venus, the atmosphere is behaving very oddly. A giant, previously unknown planet-scale wall of cloud travels westward around the planet every 4.9 days - and apparently has been doing so since at least 1983.

It can extend up to 7,500 kilometres (4,660 miles) long, stretching across the equator to both the north and south mid latitudes, at relatively low altitudes between 47.5 and 56.5 kilometres. It's a phenomenon that's never been seen anywhere else in the Solar System.

"If this happened on Earth, this would be a frontal surface at the scale of the planet," said astrophysicist Pedro Machado of the Institute of Astrophysics and Space Sciences in Portugal.

"That's incredible."

The planet-scale wave feature. (Javier Peralta/JAXA-Planet C team)

Venus is an extreme sort of place for a rocky habitable zone planet. It's completely shrouded in a thick atmosphere made up almost entirely of carbon dioxide that rotates 60 times faster than the planet itself, producing insane winds.

The atmosphere rains sulfuric acid, and its atmospheric pressure at 0 altitude is almost 100 times greater than Earth's. If that weren't bad enough, it's lander-meltingly hot, with an average surface temperature of 471 degrees Celsius (880 degrees Fahrenheit).

That cloudy atmosphere is a fascinating place, and prone to huge waves. A bow-like structure 10,000 kilometres long that comes and goes in the upper atmosphere is a stationary gravity wave, thought to be generated by the rotating atmosphere blowing up against a mountain on the surface. Anotherplanet-encircling Y-shaped wave in the cloudtops is a wave distorted by Venus' powerful winds.

But there's more. When studying infrared images taken by Japanese Venus orbiter Akatsuki between 2016 and 2018, a team of researchers led by physicist Javier Peralta of the Japanese Space Agency (JAXA) spotted a feature that looked a lot like an atmospheric wave, but at an unprecedented altitude.

The new feature is different. It's much deeper than any atmospheric wave ever seen before on Venus, occurring in the cloud layer responsible for the greenhouse effect that makes the surface so scorchingly hot.

Careful analysis, as well as a study of past observations, showed that the feature has been recurrent, but heretofore unnoticed, since at least 1983, since it could only emerge through a collection of observations from a large number of instruments over a period of time.

The planet-scale wave feature. (Javier Peralta/JAXA)

The newly identified feature, the researchers found, can span up to 7,500 kilometres, and circles the planet once every 4.9 days at a velocity of around 328 kilometres per hour (204 miles per hour). That's a little faster than the clouds at this level, which have a rotation period of about 5.7 days.

But it's still unknown what causes it.

"This atmospheric disruption is a new meteorological phenomenon, unseen on other planets. Because of this it is yet difficult to provide a confident physical interpretation," Peralta said.

Numerical simulations, however, reveal that many of the disruption's properties can be seen in a nonlinear atmospheric Kelvin wave. Here on Earth, these are large gravity waves (not to be confused with gravitational waves) that are sometimes 'trapped' at the equator and are affected by the planet's rotation.

Like Earth's Kelvin waves, the Venusian feature propagates in the same direction as the winds that circle the planet - and it has no effect on meridional winds that blow between north and south.

The feature in August 2016 (bottom left) and its evolution from 2016 to 2018 (inset). (Planet-C Project Team, NASA, IRTF)

If the feature is a Kelvin wave, that could have interesting implications. We don't, for instance, understand why Venus' atmosphere rotates so fast. Kelvin waves can interact with other kinds of atmospheric waves, such as Rossby waves.

This could have implications for the atmospheric super-rotation. And a Kelvin wave could also help us understand the relationship between Venus' surface topography and the dynamics of its atmosphere.

"Since the disruption cannot be observed in the ultraviolet images sensing the top of the clouds at about 70 kilometres height, confirming its wave nature is of critical importance," Peralta said.

"We would have finally found a wave transporting momentum and energy from the deep atmosphere and dissipating before arriving at the top of the clouds. It would therefore be depositing momentum precisely at the level where we observe the fastest winds of the so-called atmospheric super-rotation of Venus, whose mechanisms have been a long-time mystery."

More observations are currently underway, to see if more light can be shed on this mysterious wall.

The research has been published in Geophysical Research Letters.

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An Epic, Planet-Scale Wave Has Been Hiding in The Toxic Clouds of Venus For Decades - ScienceAlert

In 1950, Italian-American physicist Enrico Fermi sat down to lunch with some of his colleagues at the Los Alamos National Laboratory, where he had worked five years prior as part of the Manhattan Project. According to various accounts, the conversation turned to aliens and the recent spate of UFOs. Into this, Fermi issued a statement that would go down in the annals of history: Where is everybody?

This became the basis of the Fermi Paradox, which refers to the high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence. But despite seventy years of looking, we still havent been able to answer Fermis question, leading to multiple proposals as to why this is. Today, we look at the Aestivation Hypothesis, which argues that aliens are not dead (or non-existent), theyre just resting!

This theory takes its cue from nature, where certain organisms enter a state of prolonged torpor during particularly hot or dry periods. Similar to hibernation in the winter, these organisms will remain in this state until conditions become cooler and wetter. Applied to the Fermi Paradox, the Aestivation Hypothesis asserts that alien civilizations are largely dormant because they are awaiting better conditions.

At the heart of Fermis famous question was a discrepancy that was undeniable in his time, and hasnt changed despite seventy years of research. On the one hand, there is the assumed likelihood that extraterrestrial intelligence (ETI) is plentiful throughout the Universe. On the other, theres the lack of hard evidence attesting to their existence.

Assuming that ETIs are likely is not at all farfetched. Based on the sheer size and age of the observable Universe 93 billion light-years in diameter and 13.8 billion years scientists have typically treated the existence of extraterrestrial intelligence (ETI) as a foregone conclusion. Statistically speaking, the odds are very much in favor of their being millions of civilizations out there.

Dr. Frank Drake illustrated as much in 1961 during a meeting at the Green Bank Observatory. While addressing fellow astrophysicists and SETI researchers, he presented his famous equation for estimating the number of ETIs in our galaxy that we can communicate with at any given time. The Drake Equation, as it came to be known, was expressed mathematically as:

While most of these parameters are subject to varying degrees of uncertainty, the point of the equation is clear. Even when figured for conservatively, the results always indicate that there should be at least a few extraterrestrial intelligences (ETIs) in our galaxy that we should be able to communicate with. Unfortunately, despite decades of research and multiple dedicated SETI surveys, Fermis Paradox still holds.

As a result, multiple attempts have been made to resolve the Paradox theoretically. The first and perhaps best known is the Hart-Tipler Conjecture, named jointly for astrophysicist Michael Hart and mathematician/cosmologist Frank Tipler. This theory argues that there is no evidence of intelligent life out there because none exists.

Another is the Great Filter Hypothesis, theorized by Oxford economist Robin Hanson, who argued that while simple life may be very common, advanced life was not. In other words, there exists in the Universe some type of filter that prevents simple life from reaching the advanced stage and become an ETI that we would be capable of communicating with.

The built-in assumption in both of these cases is that ETIs do not exist, hence why we see no evidence of them. But as Carl Sagan famously remarked when addressing the possible existence of alien intelligence, the absence of evidence is not the evidence of absence. As such, many theorists have proposed alternate explanations of how ETIs can exist, but remain undetected by us.

This raises another issue, which is the notion that advanced species will be able to harness increasingly large amounts of energy over time. In his 1964 essay, titled Transmission of Information by Extraterrestrial Civilizations, Soviet/Russian astrophysicist Nikolai Kardashev proposed a three-tiered scheme for classifying extraterrestrial civilizations based on the amount of energy they could harness.

This scheme came to be known as the Kardashev Scale and consisted of the following:

Civilizations that fit these Types would be detectable by looking for signs of technological activity (aka. technosignatures). For example, a Type I Civilizations could be detectable through Direct Imaging, where astronomers would look for light reflected by massive clouds of satellites (aka. Clarke Belts) around the planet. A Type II civilization, meanwhile, would be capable of building a megastructure around its home star.

These civilizations would be capable of building what Freedom Dyson described in 1960 (what has since come to be known as a Dyson Sphere). This would allow a civilization to harness all of the energy of its sun while multiplying the amount of habitable space in their system exponentially. A Type III Civilization, meanwhile, could be easily detected by looking for signs of megastructures that encompass an entire galaxy (or parts thereof).

So it possible that the Universe if filled with civilizations ranging from Type I to Type III levels of development, but are not currently engaged in any technological activity? Thats where the concept of aestivation comes into play.

The theory was first suggested by research associates Anders Sandberg and Stuart Armstrong as well as famed astronomer, astrophysicist, and philosopher Milan Cirkovic from the Future of Humanity Institute (FHI) at the University of Oxford. In their 2017 study titled, That is Not Dead Which Can Eternal Lie: the Aestivation Hypothesis for Resolving Fermis Paradox, they proposed this as a possible resolution to the Fermi Paradox.

The study was partly based on previous research conducted by Sandberg and Armstrong in a 2013 study where they extended the Fermi Paradox beyond the Milky Way. Titled Eternity in Six Hours: Intergalactic Spreading of Intelligent Life and Sharpening the Fermi Paradox, Sandberg and Armstrong argued that an advanced civilization would be able to colonize a galaxy and even travel between galaxies with relative ease.

Having concluded that in a Universe of about 2 trillion galaxies (according to recent estimates) that has existed for 13.8 billion years, there should be many Type III Civilizations out there (based on the Kardashev Scale). Not only would these species have been able to colonize their respective galaxies in a relatively short amount of time, but have been able to reach the Milky Way by now.

The reason why this is not evidence to us, argued Sandberg and Armstrong, has to do with the Landauers Principle, which is considered by man to be the basic principle of the thermodynamics of information processing. This rule holds that any logically irreversible manipulation of information (aka. computation) must be accompanied by a corresponding entropy increase (loss of heat) for the information-processing apparatus.

Applied to megastructures like Dyson Spheres, Matrioshka Brains, etc., the level of heat energy and entropy involved would be enormous. Meanwhile, astronomy and cosmology teach us that the Universe is getting steadily cooler over time as star formation slowly dies. At the same time, cosmic expansion causes the wavelength of light to stretch, which causes momentum and energy to be lost.

Eventually, its believed that this will result in the Big Chill (or Big Freeze) scenario, where even the background radiation will cool and the Universe will experience heat death. But from a computational point of view, long before that happens, advanced species could be waiting for the Universe to cool so their megastructures are able to function more efficiently.

According to Sandberg and Armstrong, an advanced civilization could (in principle) perform exponentially more irreversible logical operations by transferring entropy to the cosmological background in the future. In fact, by waiting until the background temperature is significantly lower, they estimate that an additional ten nonillion (1030), or ten quadrillion quadrillion, more computations could be performed.

It is also possible that aestivation is a means for early arrivals to our Universe to skip the long waiting period for other intelligent species to evolve so that when they wake up, theyll have plenty of people to talk to! Considering that life capable of communicating with the cosmos took 4.5 billion years to evolve here on Earth, this makes a fair degree of sense.

Of course, the Aestivation Hypothesis (much like the Fermi Paradox and the Drake Equation) is based on some assumptions about how ETIs would behave. These include:

In short, the hypothesis assumes that given the age of the Universe enough time has passed for civilizations to emerge that are more advanced than humanity. It is also assumed that they would have become space-faring civilizations, actively colonizing neighboring star systems and possibly even neighboring galaxies.

Lastly, it is assumed that this process would be visible by looking for evidence of megastructures and massive construction processes. This would include smashing up planets for building materials, relocating stars or galaxies, or even consuming gas giants, stars, or (again) entire galaxies to create fuel.

Of course, there are drawbacks and some issues with this hypothesis that have drawn criticism from the astronomical and computational community. For starters, the theory assumes that intelligent civilizations should be plentiful and that not all civilizations will aestivate. If this is the case, then there should be at least a few civilizations that would be still detectable through their technosignatures.

Second, Charles Bennett a physicist, information theorist and Fellow at the IBM Watson Research Center along with Hanson and C. Jess Reidel (of the Perimeter Institute for Theoretical Physics) produced a rebuttal paper to the Aestivation Hypothesis in 2019. In it, they argued that Sandberg et al. implicitly assume that computer-generated entropy could only be disposed of by transferring it to the cosmological background.

According to Bennett, Hanson, and Reidel, this is based on a misunderstanding of astrophysics and the physics of computing. While such an argument might apply in the distant future, they argue, it does not apply in the present and renders the aestivation model inaccurate. As they state:

[O]ur universe today contains vast reservoirs and other physical systems in non-maximal entropy states, and computer-generated entropy can be transferred to them at the adiabatic conversion rate of one bit of negentropy to erase one bit of error. This can be done at any time, and is not improved by waiting for a low cosmic background temperature. Thus aliens need not wait to be active.

In the end, the Aestivation Hypothesis is like all other attempts to resolve the Fermi Paradox (and the Drake Equation, for that matter). Far from being a concrete answer, this theory is a thought experiment designed to bring Fermis famous question into focus and perhaps provide some testable assertions. In the end, the ultimate goal is to help refine the search for extraterrestrial intelligence (SETI).

We have written many interesting articles about the Fermi Paradox, the Drake Equation, and the Search for Extraterrestrial Intelligence (SETI) here at Universe Today.

Heres Where Are The Aliens? How The Great Filter Could Affect Tech Advances In Space, Why Finding Alien Life Would Be Bad. The Great Filter, How Could We Find Aliens? The Search for Extraterrestrial Intelligence (SETI), and Fraser and John Michael Godier Debate the Fermi Paradox.

And be sure to check out the rest of our Beyond Fermis Paradox series:

Astronomy Cast has some interesting episodes on the subject. Heres Episode 24: The Fermi Paradox: Where Are All the Aliens?, Episode 110: The Search for Extraterrestrial Intelligence, Episode 168: Enrico Fermi, Episode 273: Solutions to the Fermi Paradox.

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Beyond the Fermi Paradox V: What is the Aestivation Hypothesis? - Universe Today