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STScI | Space Telescope Science InstituteNASA

gravitational microlensing

read the mission facts below

01

The bending of light can be observed in different ways.

It can change the brightness of a background star (photometric) or its apparent position (astrometric). Einstein predicted that the photometric brightening would never be observed, due to the very close alignment required. But a few decades later, technology had improved enough that detecting such events which happen for 1 in a million stars became achievable.

02

Gravitational microlensing, as this effect is known, is now a major tool in astronomy.

The photometric effect, leading to a temporary brightening of a background star, has been used to find planets around other stars than the Sun, as well as black holes, brown dwarfs, and other low-mass objects.

03

Astrometric microlensing is now providing us with crucial additional information.

The astrometric effect, consisting of a temporary apparent deflection in the position of the background star, provides much more information about the massive object causing the microlensing effect. In 2014, the nearby white dwarf Stein 2051B passed very close to a background star, deflecting the background star’s image. A team led by astronomers at STScI in Baltimore was able to make the first observation of this light bending caused by a star other than our own Sun. Thanks to these observations, they were able to calculate the mass of this white dwarf. This measurement provided essential information on white dwarfs, the last evolutionary stage for the majority of stars.

04

Combining astrometry and photometry is also allowing us to investigate black holes in the Milky Way.

There are an estimated 100 million black holes with masses only a few times that of the Sun floating around the Milky Way. When they pass in front of stars, these black holes can also deflect light from these stars, leading to both a photometric and an astrometric effect. If detected, these signals would enable us to calculate the mass of the black holes, as well as how far away they are, and how fast they move in space. This enables us to understand the fate of stars that are too massive to become white dwarfs, and instead collapse and end their lives as black holes.

05

In the future, astrometric microlensing will play an important role in understanding how common planets like the Earth are.

The mass of planets detected by microlensing cannot always be determined very precisely with current observations. This is because photometry usually does not allow us to gather all necessary information to make these calculations. With astrometry, however we get much more precise information as to the nature of the planets and their host stars. In the future, the WFIRST mission will make routine photometric and astrometric measurement for millions of stars, leading to better mass measurements for thousands of exoplanets and their host stars. This will truly place our own Earth and Solar System into perspective.

Einstein said it first:

In his theory of General Relativity, Einstein predicted that massive objects could bend light from background stars.

A few years later, Eddington and collaborators collected observations around the world during a solar eclipse. They measured the bending of light from background stars by the Sun, proving Einstein right, and making him an international celebrity.

members

Kailash C. Sahu (PI)

Kailash C. Sahu (PI)

Jay Anderson

Jay Anderson

Andrea Bellini

Andrea Bellini

Pierre Bergeron

Pierre Bergeron

Edmund P. Nelan

Edmund P. Nelan

Thomas M. Brown

Thomas M. Brown

Annalisa Calamida

Annalisa Calamida

Stefano Casertano

Stefano Casertano

Howard E. Bond

Howard E. Bond

Laurent Pueyo

Laurent Pueyo

Noe Kains

Noe Kains

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