how many microlensing events over the course of a millennium

What are microlensing events?

Microlensing refers to the special case of GRAVITATIONAL. LENSING where the multiple images produced are too close. together on the sky to be observed as separate images. However, the lensing can still be detected because these multiple images appear as a single object of increased apparent brightness.

What is the microlensing method?

The gravitational microlensing method allows planets to be found using light from a distant star. The path of the light from this star will be altered by the presence of a massive lens – in our case, a star and a planet. Thus, for a short period of time, the distant star will appear brighter.

How many exoplanets have been discovered using gravitational microlensing?

Combining their data, they found the most likely planet mass to be 1.5 times the mass of Jupiter. As of April 2020, 89 exoplanets have been detected by this method.

What is the microlensing technique quizlet?

Microlensing. a form of gravitational lensing in which the light from a background source is bent by the gravitational field of a foreground lens to create distorted, multiple and/or brightened images.

What causes microlensing?

Gravitational microlensing relies on chance events where from our viewpoint, one star passes in front of another star. The farther star is usually a bright star, and the near one is normally one we couldn't ordinarily see from Earth.

What is microlensing survey?

In particular, microlensing is sensitive to very low-mass planets on wide orbits and free-floating planets, and can be used to search for planets orbiting host stars with a broad range of masses and Galactocentric distances.

What planets have been discovered using gravitational microlensing?

(Phys.org)—Astronomers have found a new massive alien world using the gravitational microlensing technique. The newly detected exoplanet, designated MOA-2016-BLG-227Lb, is about three times more massive than Jupiter and orbits a distant star approximately 21,000 light years away. The finding was published Apr.

What is the name of the first exoplanet discovered?

The first exoplanet discovered was in 1992 and, since then, most exoplanets found have been less than 3,000 light-years from Earth. But M51-ULS-1b, orbiting 28 million light-years away, would be the first exoplanet ever found in another galaxy.

How many exoplanets have been directly imaged?

As of April 2020, 50 exoplanets had been discovered with direct imaging.

What is the astrometric method used in searches for planets orbiting stars other than the Sun?

What is the astrometric method used in searches for planets orbiting stars other than the Sun? using Newton's law of gravity, using the measured distance from the star and its gravitational pull on the star.

How is the astrometric technique different than the radial velocity technique of finding exoplanets?

Unlike the radial velocity method, it does not require an accurate spectrum of a star, and therefore can be used more easily to find planets around fast-rotating stars and more distant stars. One of the biggest disadvantages of this method is that the light variation effect is very small.

What type of search technique has discovered the second largest number of exoplanets?

The blue waves have a higher frequency than the red light waves. Image via NASA. Some planets are found via the wobble method. The second-most-used path to discovering exoplanets is via Doppler spectroscopy, sometimes called the radial velocity method, and commonly known as the wobble method.

How many exoplanets have been discovered?

This is a list of exoplanets. As of 1 September 2022, there are 5,157 confirmed exoplanets in 3,804 planetary systems, with 833 systems having more than one planet. Most of these were discovered by the Kepler space telescope.

How many exoplanets have been discovered using radial velocity?

The Exoplanet Archive's collection of known exoplanets were discovered using a variety of methods, and many have been detected using multiple methods....Confirmed Exoplanet Statistics.Discovery MethodNumber of PlanetsAstrometry2Imaging61Radial Velocity935Transit38977 more rows

What methods are used to find exoplanets?

Bottom line: The most popular methods of discovering exoplanets are the transit method and the wobble method, also know as radial velocity. A few exoplanets have been discovered by direct imaging and microlensing.

Why does the detection of exoplanets by gravitational lensing effectively rely on chance?

Essentially, this method relies on the gravitational force of distant objects to bend and focus light coming from a star. As a planet passes in front of the star relative to the observer (i.e. makes a transit), the light dips measurably, which can then be used to determine the presence of a planet.

How to get more information from microlensing?

Another way to get more information from microlensing events involves measuring the astrometric shifts in the source position during the course of the event and even resolving the separate images with interferometry. The first successful resolution of microlensing images was achieved with the GRAVITY instrument on the Very Large Telescope Interferometer (VLTI).

Why is microlensing so rare?

In practice, because the alignment needed is so precise and difficult to predict, microlensing is very rare. Events, therefore, are generally found with surveys, which photometrically monitor tens of millions of potential source stars, every few days for several years. Dense background fields suitable for such surveys are nearby galaxies, such as the Magellanic Clouds and the Andromeda galaxy, and the Milky Way bulge. In each case, the lens population studied comprises the objects between Earth and the source field: for the bulge, the lens population is the Milky Way disk stars, and for external galaxies, the lens population is the Milky Way halo, as well as objects in the other galaxy itself. The density, mass, and location of the objects in these lens populations determines the frequency of microlensing along that line of sight, which is characterized by a value known as the optical depth due to microlensing. (This is not to be confused with the more common meaning of optical depth, although it shares some properties.) The optical depth is, roughly speaking, the average fraction of source stars undergoing microlensing at a given time, or equivalently the probability that a given source star is undergoing lensing at a given time. The MACHO project found the optical depth toward the LMC to be 1.2×10 −7, and the optical depth toward the bulge to be 2.43×10 −6 or about 1 in 400,000.

How does microlensing affect brightness?

This function has several important properties. A (u) is always greater than 1, so microlensing can only increase the brightness of the source star, not decrease it . A (u) always decreases as u increases, so the closer the alignment, the brighter the source becomes. As u approaches infinity, A (u) approaches 1, so that at wide separations, microlensing has no effect. Finally, as u approaches 0, for a point source A (u) approaches infinity as the images approach an Einstein ring. For perfect alignment (u = 0), A (u) is theoretically infinite. In practice, real-world objects are not point sources, and finite source size effects will set a limit to how large an amplification can occur for very close alignment, but some microlensing events can cause a brightening by a factor of hundreds.

What is ideally aligned microlensing?

Ideally aligned microlensing produces a clear buffer between the radiation from the lens and source objects. It magnifies the distant source, revealing it or enhancing its size and/or brightness. It enables the study of the population of faint or dark objects such as brown dwarfs, red dwarfs, planets, white dwarfs, neutron stars, black holes, and massive compact halo objects. Such lensing works at all wavelengths, magnifying and producing a wide range of possible warping for distant source objects that emit any kind of electromagnetic radiation.

When was gravitational lensing first observed?

Gravitational lensing was first observed in 1979 , in the form of a quasar lensed by a foreground galaxy. That same year Kyongae Chang and Sjur Refsdal showed that individual stars in the lens galaxy could act as smaller lenses within the main lens, causing the source quasar's images to fluctuate on a timescale of months, also known as Chang–Refsdal lens. Bohdan Paczyński first used the term "microlensing" to describe this phenomenon. This type of microlensing is difficult to identify because of the intrinsic variability of quasars, but in 1989 Mike Irwin et al. published detection of microlensing in Huchra's Lens .

What is the purpose of microlensing?

Microlensing has also been proposed as a means to find dark objects like brown dwa rfs and black holes, study starspots, measure stellar rotation, and probe quasars including their accretion disks. Microlensing was used in 2018 to detect Icarus, the most distant star ever observed.

What is gravitational microlensing?

Gravitational microlensing is an astronomical phenomenon due to the gravitational lens effect. It can be used to detect objects that range from the mass of a planet to the mass of a star, regardless of the light they emit. Typically, astronomers can only detect bright objects that emit much light ( stars) or large objects that block background light (clouds of gas and dust). These objects make up only a minor portion of the mass of a galaxy. Microlensing allows the study of objects that emit little or no light.

What is the effect of microlensing?

Image: The Planetary Society. Microlensing is an astronomical effect predicted by Einstein's General Theory of Relativity. According to Einstein, when the light emanating from a star passes very close to another star on its way to an observer on Earth, the gravity of the intermediary star will slightly bend the light rays from the source star, ...

When did the microlensing light curve peak?

The microlensing light curve of planet OGLE–2005-BLG-390Lb The general curve shows the microlensing event peaking on July 31, 2005, and then diminishing. The disturbance around August 10 indicates the presence of a planet. Image: European Southern Observatory

What is the network of telescopes that detect microlensing events?

Whenever OGLE and MOA detect a microlensing event, it contacts a network of telescopes that specialize in searching for signs of the presence of a planet. The networks, known as Robonet, MicroFUN (the Microlensing Follow-Up Network), and PLANET (the Probing Lensing Anomalies NETwork), include 1- and 2- meter telescopes across the globe. Together, the telescopes are able to continuously cover each microlensing event, providing an accurate light curve and indicating whether a planet is present or not.

What does the lensing star do in the fourth image?

In the fourth image from the right the planet adds its own microlensing effect, creating the two characteristic spikes in the light curve. Image: OGLE.

How many planets can be detected by microlensing?

Finally, like transit photometry, microlensing searches are massive, targeting tens of thousands of planets simultaneously. If a microlensing event takes place anywhere within the observed starfield, it will be detected.

How many exoplanets are there in the MOA?

As of February 2020 it had yielded 24 exoplanets.

How long does it take for a lensing star to change its brightness?

The resulting effect is a sudden dramatic increase in the brightness of the lensing star, by as much as 1,000 times. This typically lasts for a few weeks or months before the source star moves out of alignment with the lensing star and the brightness subsides.

Overview

Mathematics

The mathematics of microlensing, along with modern notation, are described by Gould and we use his notation in this section, though other authors have used other notation. The Einstein radius, also called the Einstein angle, is the angular radius of the Einstein ring in the event of perfect alignment. It depends on the lens mass M, the distance of the lens dL, and the distance of the source dS:

How it works

Observing microlensing

History

Extreme microlensing events

Detection of extrasolar planets

Microlensing experiments

Introduction

• So far we've concluded that although we cannot resolve the individual images created during microlensing, we might detect these events from the amplification of the source. But the alignment required between observer, lens and source for an event is extremely tight, so what are the odds of this ever happening?

See more on microlensing-source.org

"Threshold" Amplification

Optical Depth to Microlensing

Measurements of The Microlensing Optical Depth