The Egg Nebula is a preplanetary nebula, created by a dying star in the process of becoming a planetary nebula. Planetary nebulas have nothing to do with planets – the name arose when 18th century astronomers spotted them in their telescopes and thought they looked like planets. Instead, they are the remnants of material expelled by Sun-like stars in the later stages of their lives.
The preplanetary nebula phase is extremely short-lived in astronomical terms – only a few thousand years. This makes them rare objects and, combined with the fact that they are quite faint, rather difficult to spot. The Egg Nebula, located around 3000 light years from us, was the first of its kind to be discovered in the 1970s. This image is based on observations performed in the mid 1990s by the Wide Field and Planetary Camera 2 (WFPC2) on the NASA/ESA Hubble Space Telescope.
During the preplanetary nebula phase, the central star periodically sheds its outer layers, which are then illuminated by the dying star at the centre. Eventually the star stops shedding material and the core remnant heats up, exciting the expelled gas so that it glows brightly and becomes a planetary nebula.
The dark band, sweeping beams, and criss-crossing arcs in this image can reveal a lot about the complex environment of a dying star. The central band is a cocoon of dust hiding the star from view.
Beams of light emanate from the obscured star, and it is thought that they are due to starlight escaping from the ring-shaped holes in the dusty cocoon that surrounds the star. The holes are possibly carved by a high-speed stream of matter, although the cause of these jets are unknown. The spoke-like features are shadows cast by blobs of material within the region of the holes in the cocoon.
Numerous bright arcs intersect the beams: these are shells of matter ejected by the star. The arcs are like tree rings, and can tell us something about the object's age as they reveal that the rate of mass ejection has varied between 100 and 500 years throughout its 10 000 year history. The gas is expanding at a rate of 20 km/s and matter has been detected out to a radius of 0.6 light years, providing an estimate of the amount of matter in the nebula.
The Copernicus Sentinel-2 mission takes us over one of the most remote islands in the world: Easter Island. Located in the Pacific Ocean, over 3500 km off the west coast of South America, this Chilean island is also known as Rapa Nui by its original inhabitants. The island was given its current name the day Europeans arrived in the 1700s – on Easter Sunday.
The island is famous for its monolithic stone statues, called Moai, said to honour the memory of the inhabitants’ ancestors. There are nearly 1000 scattered around the island, usually positioned near freshwater. Many are located near the Rano Raraku volcano, on the southeast coast. The white edges along the southern coast show the harsh waves colliding with the shore.
An interesting feature of the image is the ochre-orange colour of the Poike – the peninsula on the eastern end of the island. In ancient times, it is said that there was a lot of vegetation on the island. However, land clearing for cultivation and the Polynesian rat played a role in deforestation, leading to the erosion of the soil, particularly in the east.
Several reforestation projects have been attempted, including a eucalyptus plantation in the middle of the island, visible in dark green. The brown patch to the right of the plantation is likely to be a burn scar from a wildfire.
The majority of the island’s inhabitants live in Hanga Roa, the main town and harbour on the west coast, clearly visible in the image. Interestingly, the long runway of the island’s only airport was once designated as an emergency landing site for the US space shuttle.
At the very edge of the southwest tip of the island lies Ranu Kao, the largest volcano on the island. Its shape is distinctive owing to its crater lake, one of the island’s only three natural bodies of water.
Many tourists are drawn to the island for its mysterious history and isolated position. What is relatively unknown is the existence of two small beaches on the northeast coast. Anakena beach has white, coral sand, while the smaller Ovahe beach, surrounded by cliffs, has pink sand.
Copernicus Sentinel-2 is a two-satellite mission. Each satellite carries a high-resolution camera that images Earth’s surface in 13 spectral bands. Data from Copernicus Sentinel-2 can help monitor changes in land cover.
This image, which was captured on 7 April 2019, is also featured on the Earth from Space video programme.
This incredible image of the hourglass-shaped Southern Crab Nebula was taken to mark the NASA/ESA Hubble Space Telescope’s 29th anniversary in space. The nebula, created by a binary star system, is one of the many objects that Hubble has demystified throughout its productive life. This new image adds to our understanding of the nebula and demonstrates the telescope’s continued capabilities.
The giant 121-segment mirror array used to reflect simulated sunlight into the largest vacuum chamber in Europe seen being hoisted into position within ESA’s technical heart back in 1986.
This mirror array remains an integral element of ESA’s Large Space Simulator at the ESTEC Test Centre in Noordwijk, the Netherlands. It is used to subject entire satellites to space-like conditions ahead of launch. At 15 m high and 10 m in diameter, the chamber is cavernous enough to accommodate an upended double decker bus.
Satellites are lowered down through a topside hatch. Once the top and side hatches are sealed, high-performance pumps create a vacuum a billion times lower than standard sea level atmosphere, held for weeks at a time during test runs.
This mirror array is made of 121 separate hexagonal segments. Its task is to reflect a 6-m diameter beam of simulated sunlight into the chamber, at the same time as the walls are pumped full of –190°C liquid nitrogen, together recreating the extreme thermal conditions prevailing in orbit.
By re-orienting the individual segments a much tighter beam can be focused, helping to simulate higher intensity sunlight, such as the 10 solar constants experienced in the vicinity of Sun-scorched Mercury, for testing the ESA/JAXA BepiColombo mission.
In preparation for his Beyond mission, ESA astronaut Luca Parmitano was at the Johnson Space Center in Houston, USA, in March 2019. Here he is strapped to the Partial Gravity Simulator to practice repairing the dark-matter hunter AMS-02.
AMS-02, the Alpha Magnetic Spectrometer, consists of seven instruments that monitor cosmic rays from space. The 6918 kg instrument was installed in 2011 and results hint at a new phenomenon that may reveal more about the invisible ‘dark matter’.
The facility was only meant to run for only three years, but it has been so successful that the International Space Station partners and scientific community wish to extend its working life. Despite this, three of the four cooling pumps have stopped working and need to be repaired – this is where Luca comes in.
At the Space Vehicle Mock-up Facility in ‘Building 9’ Luca is testing tools, procedures and techniques to replace the cooling system during a series of spacewalks planned for this year. AMS-02 was never designed to be repaired in space so each aspect of the spacewalk needs to be considered and practiced in detail.
EDRS-C is currently in the anechoic test chamber at the Compact
Antenna Test Range at Airbus in Ottobrunn Germany, where the satellite is currently
undergoing verification of the antennas performance before shipment to its launch site in Kourou in June.
The European Data Relay System (EDRS) is designed to relay data between satellites in
low orbit and Earth via satellites in geostationary orbit. It allows transmission of large quantities of data with reduced delay, using innovative laser communication technology.
It is a new, independent European satellite system, and is a public–private partnership
between ESA and Airbus (DE) as part of ESA’s efforts to federate industry around large-
scale programmes, stimulating technology developments and achieving economic
EDRS will form the ‘SpaceDataHighway’for Europe, made up of one hosted data-relay
payload (EDRS-A), one data-relay payload on a dedicated satellite (EDRS-C) and a
dedicated ground segment.
EDRS dramatically increases the speed with which low-orbiting satellites can deliver
their information to users, by relaying their data via the EDRS payloads in geostationary orbit to European ground stations.
With EDRS ground stations in Redu (BE), Harwell (UK) and two in Weilheim (DE) plus
the Italian Space Agency’s user ground station in Matera (IT), EDRS is the first truly European laser communications network.
Most globular clusters are almost perfectly spherical collections of stars — but Messier 62 breaks the mould. The 12-billion-year-old cluster is distorted, and stretches out on one side to form a comet-like shape with a bright head and extended tail. As one of the closest globular clusters to the centre of our galaxy, Messier 62 is likely affected by strong tidal forces that displace many of its stars, resulting in this unusual shape.
When globular clusters form, they tend to be somewhat denser towards the centre. The more massive the cluster, the denser the centre is likely to be. With a mass with almost a million times that of the Sun, Messier 62 is one of the densest of them all. With so many stars at the centre, interactions and mergers occur regularly. Huge stars form and run out of fuel quickly, exploding violently and their remains collapse to form white dwarfs, neutron stars and even black holes!
For many years, it was believed that any black holes that form in a globular cluster would quickly be kicked out due to the violent interactions taking place there. However, in 2013, a black hole was discovered in Messier 62 — the first ever to be found in a Milky Way globular cluster, giving astronomers a whole new hunting ground for these mysterious objects.
This view comprises ultraviolet and visible light gathered by the NASA/ESA Hubble Space Telescope’s Advanced Camera for Surveys.
Week in images
15 - 19 April 2019