Waltzing dwarfs: This seemingly unspectacular series of dots with varying distances between them actually shows the slow waltz of two brown dwarfs. The image is a stack of 12 images made over the course of three years with the NASA/ESA Hubble Space Telescope. Using high-precision astrometry, an Italian-led team of astronomers tracked the two components of the system as they moved both across the sky and around each other. The observed system, Luhman 16AB, is only about six light-years away and is the third closest stellar system to Earth — after the triple star system Alpha Centauri and Barnard’s Star. Despite its proximity, Luhman 16AB was only discovered in 2013 by the astronomer Kevin Luhman. The two brown dwarfs that make up the system, Luhman 16A and Luhman 16B, orbit each other at a distance of only three times the distance between the Earth and the Sun, and so these observations are a showcase for Hubble’s precision and high resolution. The astronomers using Hubble to study Luhman 16AB were not only interested in the waltz of the two brown dwarfs, but were also searching for a third, invisible, dancing partner. Earlier observations with ESO’s Very Large Telescope indicated the presence of an exoplanet in the system. The team wanted to verify this claim by analysing the movement of the brown dwarfs in great detail over a long period of time, but the Hubble data showed that the two dwarfs are indeed dancing alone, unperturbed by a massive planetary companion.

Name: Luhman 16A, Luhman 16AB, Luhman 16B
Type: Milky Way : Star : Type : Brown Dwarf
Category: Stars
Distance: 6 light years
Release date: 5 June 2017, 06:00
Credit: ESA/Hubble & NASA, L. Bedin et al.

Einstein revisited: A century ago, Albert Einstein published his famous theory of relativity. He proposed that all objects physically warp the fabric of space, with larger masses producing a more pronounced effect, and very massive objects (such as the Sun) causing light to travel along curved paths through space. Such an effect was first observed during the 1919 solar eclipse by English astronomer Arthur Eddington. Researchers had to wait a century, however, to get a telescope powerful enough to detect this gravitational microlensing caused by a star outside the Solar System. Even around objects with very large masses, such as stars, this effect is very slight, making such detections extremely challenging for ground-based telescopes. It is, however, within the capabilities of the NASA/ESA Hubble Space Telescope, which gathered the data comprising this Picture of the Week. The bright star in the centre of the image is the nearby white dwarf Stein 2051B, only 17 light-years from Earth. The smaller star below is about 5000 light-years away. Astronomers observed Stein 2051B eight times within two years while the white dwarf travelled in front of of the distant background star. During the close alignment, the white dwarf’s gravity bent the light from the distant star, making it appear offset by about 2 milliarcseconds from its actual position. This deviation is so small that it is equivalent to observing an ant crawl across the surface of a 1€ coin from 2300 kilometres away.

Name: Stein 2051
Type: Milky Way : Star : Evolutionary Stage : White Dwarf
Category: Stars
Constellation: Camelopardalis
Distance: 18 light years
Release date: 12 June 2017, 06:00
Credit: NASA, ESA, and K. Sahu (STScI)

Binary star system Stein 2051 (annotated): This NASA/ESA Hubble Space Telescope image shows the binary star system Stein 2051 on October 1, 2013, consisting of the brighter, redder "A" component at lower right and the fainter, bluer "B" component near the centre, a white dwarf star. Because these stars are only 17 light-years away they appear to move in the sky relative to the much more distant background stars in several months of observations with Hubble. The wavy blue line traces this motion, due to their true motion relative to the Sun combined with the parallax due to the motion of Earth around the Sun. Stein 2051 B appeared to pass close enough to one of these background stars, labeled "source" that the light from the background star was bent due to the mass of the white dwarf. This colour image was made by combining images taken in two filters with Hubble's Wide Field Camera 3.

Name: Stein 2051
Type: Milky Way : Star : Evolutionary Stage : White Dwarf
Category: Stars
Distance: 18 light years
Release date: 12 June 2017, 06:00
Credit: NASA, ESA, and K. Sahu (STScI)

Hubble measures deflection of starlight by a foreground Object: This illustration reveals how the gravity of a white dwarf warps space and bends the light of a distant star behind it. White dwarfs are the burned-out remnants of normal stars. The NASA/ESA Hubble Space Telescope captured images of the dead star, called Stein 2051 B, as it passed in front of a background star. During the close alignment, Stein 2051 B deflected the starlight, which appeared offset by about 2 milliarcseconds from its actual position. This deviation is so small that it is equivalent to observing an ant crawl across the surface of a 1€ coin from 2300 kilometres away. From this measurement, astronomers calculated that the white dwarf's mass is roughly 68 percent of the sun's mass. Stein 2051 B resides 17 light-years from Earth. The background star is about 5000 light-years away. The white dwarf is named for its discoverer, Dutch Roman Catholic priest and astronomer Johan Stein.

Name: Stein 2051
Type: Milky Way : Star : Evolutionary Stage : White Dwarf
Category: Stars
Release date: 12 June 2017, 06:00
Credit: NASA, ESA, and A. Feild (STScI)

What’s in a name?: Not all galaxies have the luxury of possessing a simple moniker or quirky nickname. The subject of this NASA/ESA Hubble Space Telescope image was one of the unlucky ones, and goes by the rather unpoetic name of 2XMM J143450.5+033843. Such a name may seem like a random jumble of numbers and letters, but like all galactic epithets it has a distinct meaning. This galaxy, for example, was detected and observed as part of the second X-ray sky survey performed by ESA’s XMM-Newton Observatory. Its celestial coordinates form the rest of the bulky name, following the “J”: a right ascension value of 14h 34m 50.5s (this can be likened to terrestrial longitude), and a declination of +03d 38m 43s (this can be likened to terrestrial latitude). The other fuzzy object in the frame was named in the same way — it is a bright galaxy named 2XMM J143448.3+033749. 2XMM J143450.5+033843 lies nearly 400 million light-years away from Earth. It is a Seyfert galaxy that is dominated by something known as an Active Galactic Nucleus — its core is thought to contain a supermassive black hole that is emitting huge amounts of radiation, pouring energetic X-rays out into the Universe.

Name: 2XMM J143450.5+033843
Type: Local Universe : Galaxy : Activity : AGN : Seyfert
Category: Galaxies
Constellation: Virgo
Distance: 400 million light years
Release date: 26 June 2017, 06:00
Credit: ESA/Hubble & NASA