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  • richardmitnick 4:08 pm on March 26, 2021 Permalink | Reply
    Tags: "The Milky Way’s Local Arm Is Longer Than We Thought", , , , , Gaia EDR3, ,   

    From European Space Agency [Agence spatiale européenne] [Europäische Weltraumorganisation](EU) via Sky & Telescope : “The Milky Way’s Local Arm Is Longer Than We Thought” 

    ESA Space For Europe Banner

    From European Space Agency – United Space in Europe (EU)
    From European Space Agency [Agence spatiale européenne] [Europäische Weltraumorganisation](EU)


    Sky & Telescope

    March 23, 2021
    Monica Young

    The ancients gazed at the Milky Way for millennia, but it wasn’t until the mid-20th century that we discovered we live in a galaxy that takes a spiral shape.

    New maps of the Milky Way suggest the Local Arm that we call home is longer than expected, now upgraded to a major spiral feature (but not quite an arm).

    This artist’s concept shows our Milky Way galaxy, but recent studies suggest the Local Arm might be longer than what’s depicted here. Credit: R. Hurt / National Aeronautics Space Agency(USA)/
    JPL-Caltech /

    But while astronomers now generally agree that our spiral has four major arms, what they actually look like is still open to question. That includes the Local Arm that we call home (which may or may not be an arm at all).

    Two recent studies of the latest data release from the European Space Agency’s Gaia mission suggest our part of the spiral might not be as rural as once thought. The Local Arm gets an upgrade to a major spiral feature in the new maps, published in the January Astronomy & Astrophysics and also separately Astronomy & Astrophysics, respectively.

    Mapping the Milky Way

    Determining the details of galactic structure is difficult because we’re mapping our galaxy from within, which is a bit like trying to tell what kind of plane you’re flying in by looking out the tiny porthole window. Not only is a bird’s-eye view forever out of reach, there’s also interstellar material blocking our view.

    Even with those limitations in mind, how we see our galaxy depends on what we’re looking at. Some studies have measured 21-centimeter radio waves from hydrogen gas that suffuses the galaxy, the fuel for new star formation. Other studies have mapped hydrogen gas ionized by ultraviolet emission pouring out of stellar newborns. Still others look at radio masers, which trace shocks driven by young stellar winds.

    Astronomers have used all these methods to trace stellar nurseries, which mark spiral arms in other galaxies and presumably our own. But it’s a case of blind men examining the proverbial elephant. Studies differ on the length and angles of the arms. The nature of the Local Arm also depends on the technique used to measure it.

    With the advent of the Gaia mission, which is mapping exact positions and motions of a billion stars, Milky Way maps have experienced something of a renaissance. In recent months, two independent teams have set out to recast the local spiral structure: one led by Ye Xu (Purple Mountain Observatory (CN), Chinese Academy of Sciences(CN)) and the other by Eloisa Poggio (University of Côte d’Azur [Université Côte d’Azur](FR)).

    Xu and his colleagues used the latest Gaia data release [EDR3] to select almost 10,000 stars of spectral type O to B2, massive and brilliant stars that are at most 20 million years old and thus not too far from their birthplaces in the spiral arms.

    Meanwhile, Poggio and her colleagues mapped more than 750,000 of the most massive main-sequence stars, almost 700 newborn star clusters, and nearly 2,000 young Cepheid variables, giant pulsating stars with well-known distances. This team is working with more objects and thus has better statistics. But the stars and stellar groups are all somewhat older (though still less than 100 million years old); with more time to travel away from the spiral arm they were born in, they give a fuzzier view of the spiral structure.

    A Longer Local Arm, and a Less Grand Milky Way

    Despite their differences, both studies find that the Local Arm is longer than expected, between 23,000 and 26,000 light-years long. The finding upgrades it to a major spiral feature, if not quite a full-size arm.

    The Milky Way’s spiral structure near the Sun is divided into four spiral features (from the inner galaxy out): the Scutum-Centaurus Arm (green), the Sagittarius-Carina Arm (purple), the Local Arm (blue), and the Perseus Arm (black). Radio masers (triangles) trace the arms most faithfully due to their youth, but masers only cover a third of the Milky Way. Xu’s team turned to the most massive O and B stars (red) to add more data, tracing out a longer Local Arm than expected. In the team’s data, the Local Arm appears to bend inward toward the left. Credit: Xu et al.https://www.aanda.org/articles/aa/full_html/2021/01/aa40103-20/aa40103-20.html.

    But the teams still don’t agree on what the Local Arm looks like. While Xu’s team finds that the arm might bend, spiraling inward, the map made by Poggio’s team shows it as a nearly straight line. The Local Arm may also have a large gap, which makes it hard to identify different sections that belong to it, says Mark Reid (Harvard Smithsonian Center for Astrophysics(US)), who was not involved in the study.

    “Spiral arms do not have a single, constant pitch angle,” Reid explains. “Instead, they appear to be formed out of segments which have markedly different pitch angles.”

    Astronomers have long thought that spiral arms form via density waves, in which stars circling the galactic center pile up in spiral-shaped traffic jams. While many stars are born in the traffic jam, they eventually sail through, but the traffic jam stays in place.

    However, the raggedy shape of the Milky Way’s arms, including the Local Arm’s segmentation, could point to a different scenario, one in which clumps of stars form and then elongate into arm segments. Those segments join up to form longer arms, but there’s no true spiral shape that’s maintained over time.

    The same mechanism isn’t necessarily at work everywhere; two-armed “grand-design” spirals might still originate as traffic jams. But evidence suggests that Milky Way is not of the grand-design variety.

    As Gaia continues to deliver increasingly precise measurements of stars’ positions in our galaxy, especially the younger and fainter (and thus more distant) ones, astronomers will be able to confirm the details of the arm we live in, as well as the other arms of the Milky Way.

    See the full article here .

    Please help promote STEM in your local schools.

    Stem Education Coalition

    From European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

    ESA’s space flight programme includes human spaceflight (mainly through participation in the International Space Station program); the launch and operation of uncrewed exploration missions to other planets and the Moon; Earth observation, science and telecommunication; designing launch vehicles; and maintaining a major spaceport, the The Guiana Space Centre [Centre Spatial Guyanais; CSG also called Europe’s Spaceport) at Kourou, French Guiana. The main European launch vehicle Ariane 5 is operated through Arianespace with ESA sharing in the costs of launching and further developing this launch vehicle. The agency is also working with NASA to manufacture the Orion Spacecraft service module that will fly on the Space Launch System.

    The agency’s facilities are distributed among the following centres:

    ESA science missions are based at ESTEC in Noordwijk, Netherlands;
    Earth Observation missions at ESA Centre for Earth Observation in Frascati, Italy;
    ESA Mission Control (ESOC) is in Darmstadt, Germany;
    the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany;
    the European Centre for Space Applications and Telecommunications (ECSAT), a research institute created in 2009, is located in Harwell, England;
    and the European Space Astronomy Centre (ESAC) is located in Villanueva de la Cañada, Madrid, Spain.

    The European Space Agency Science Programme is a long-term programme of space science and space exploration missions.


    After World War II, many European scientists left Western Europe in order to work with the United States. Although the 1950s boom made it possible for Western European countries to invest in research and specifically in space-related activities, Western European scientists realized solely national projects would not be able to compete with the two main superpowers. In 1958, only months after the Sputnik shock, Edoardo Amaldi (Italy) and Pierre Auger (France), two prominent members of the Western European scientific community, met to discuss the foundation of a common Western European space agency. The meeting was attended by scientific representatives from eight countries, including Harrie Massey (United Kingdom).

    The Western European nations decided to have two agencies: one concerned with developing a launch system, ELDO (European Launch Development Organization), and the other the precursor of the European Space Agency, ESRO (European Space Research Organisation). The latter was established on 20 March 1964 by an agreement signed on 14 June 1962. From 1968 to 1972, ESRO launched seven research satellites.

    ESA in its current form was founded with the ESA Convention in 1975, when ESRO was merged with ELDO. ESA had ten founding member states: Belgium, Denmark, France, West Germany, Italy, the Netherlands, Spain, Sweden, Switzerland, and the United Kingdom. These signed the ESA Convention in 1975 and deposited the instruments of ratification by 1980, when the convention came into force. During this interval the agency functioned in a de facto fashion. ESA launched its first major scientific mission in 1975, Cos-B, a space probe monitoring gamma-ray emissions in the universe, which was first worked on by ESRO.

    ESA50 Logo large

    Later activities

    ESA collaborated with National Aeronautics Space Agency on the International Ultraviolet Explorer (IUE), the world’s first high-orbit telescope, which was launched in 1978 and operated successfully for 18 years. A number of successful Earth-orbit projects followed, and in 1986 ESA began Giotto, its first deep-space mission, to study the comets Halley and Grigg–Skjellerup. Hipparcos, a star-mapping mission, was launched in 1989 and in the 1990s SOHO, Ulysses and the Hubble Space Telescope were all jointly carried out with NASA. Later scientific missions in cooperation with NASA include the Cassini–Huygens space probe, to which ESA contributed by building the Titan landing module Huygens.

    As the successor of ELDO, ESA has also constructed rockets for scientific and commercial payloads. Ariane 1, launched in 1979, carried mostly commercial payloads into orbit from 1984 onward. The next two versions of the Ariane rocket were intermediate stages in the development of a more advanced launch system, the Ariane 4, which operated between 1988 and 2003 and established ESA as the world leader in commercial space launches in the 1990s. Although the succeeding Ariane 5 experienced a failure on its first flight, it has since firmly established itself within the heavily competitive commercial space launch market with 82 successful launches until 2018. The successor launch vehicle of Ariane 5, the Ariane 6, is under development and is envisioned to enter service in the 2020s.

    The beginning of the new millennium saw ESA become, along with agencies like National Aeronautics Space Agency(US), Japan Aerospace Exploration Agency, Indian Space Research Organisation, the Canadian Space Agency(CA) and Roscosmos(RU), one of the major participants in scientific space research. Although ESA had relied on co-operation with NASA in previous decades, especially the 1990s, changed circumstances (such as tough legal restrictions on information sharing by the United States military) led to decisions to rely more on itself and on co-operation with Russia. A 2011 press issue thus stated:

    “Russia is ESA’s first partner in its efforts to ensure long-term access to space. There is a framework agreement between ESA and the government of the Russian Federation on cooperation and partnership in the exploration and use of outer space for peaceful purposes, and cooperation is already underway in two different areas of launcher activity that will bring benefits to both partners.”

    Notable ESA programmes include SMART-1, a probe testing cutting-edge space propulsion technology, the Mars Express and Venus Express missions, as well as the development of the Ariane 5 rocket and its role in the ISS partnership. ESA maintains its scientific and research projects mainly for astronomy-space missions such as Corot, launched on 27 December 2006, a milestone in the search for exoplanets.

    On 21 January 2019, ArianeGroup and Arianespace announced a one-year contract with ESA to study and prepare for a mission to mine the Moon for lunar regolith.


    The treaty establishing the European Space Agency reads:

    The purpose of the Agency shall be to provide for and to promote, for exclusively peaceful purposes, cooperation among European States in space research and technology and their space applications, with a view to their being used for scientific purposes and for operational space applications systems…

    ESA is responsible for setting a unified space and related industrial policy, recommending space objectives to the member states, and integrating national programs like satellite development, into the European program as much as possible.

    Jean-Jacques Dordain – ESA’s Director General (2003–2015) – outlined the European Space Agency’s mission in a 2003 interview:

    “Today space activities have pursued the benefit of citizens, and citizens are asking for a better quality of life on Earth. They want greater security and economic wealth, but they also want to pursue their dreams, to increase their knowledge, and they want younger people to be attracted to the pursuit of science and technology. I think that space can do all of this: it can produce a higher quality of life, better security, more economic wealth, and also fulfill our citizens’ dreams and thirst for knowledge, and attract the young generation. This is the reason space exploration is an integral part of overall space activities. It has always been so, and it will be even more important in the future.”


    According to the ESA website, the activities are:

    Observing the Earth
    Human Spaceflight
    Space Science
    Space Engineering & Technology
    Telecommunications & Integrated Applications
    Preparing for the Future
    Space for Climate


    Copernicus Programme
    Cosmic Vision
    Horizon 2000
    Living Planet Programme


    Every member country must contribute to these programmes:

    Technology Development Element Programme
    Science Core Technology Programme
    General Study Programme
    European Component Initiative


    Depending on their individual choices the countries can contribute to the following programmes, listed according to:

    Earth Observation
    Human Spaceflight and Exploration
    Space Situational Awareness


    ESA has formed partnerships with universities. ESA_LAB@ refers to research laboratories at universities. Currently there are ESA_LAB@

    Technische Universität Darmstadt
    École des hautes études commerciales de Paris (HEC Paris)
    Université de recherche Paris Sciences et Lettres
    University of Central Lancashire

    Membership and contribution to ESA

    By 2015, ESA was an intergovernmental organisation of 22 member states. Member states participate to varying degrees in the mandatory (25% of total expenditures in 2008) and optional space programmes (75% of total expenditures in 2008). The 2008 budget amounted to €3.0 billion whilst the 2009 budget amounted to €3.6 billion. The total budget amounted to about €3.7 billion in 2010, €3.99 billion in 2011, €4.02 billion in 2012, €4.28 billion in 2013, €4.10 billion in 2014 and €4.33 billion in 2015. English is the main language within ESA. Additionally, official documents are also provided in German and documents regarding the Spacelab are also provided in Italian. If found appropriate, the agency may conduct its correspondence in any language of a member state.

    Non-full member states
    Since 2016, Slovenia has been an associated member of the ESA.

    Latvia became the second current associated member on 30 June 2020, when the Association Agreement was signed by ESA Director Jan Wörner and the Minister of Education and Science of Latvia, Ilga Šuplinska in Riga. The Saeima ratified it on July 27. Previously associated members were Austria, Norway and Finland, all of which later joined ESA as full members.

    Since 1 January 1979, Canada has had the special status of a Cooperating State within ESA. By virtue of this accord, the Canadian Space Agency takes part in ESA’s deliberative bodies and decision-making and also in ESA’s programmes and activities. Canadian firms can bid for and receive contracts to work on programmes. The accord has a provision ensuring a fair industrial return to Canada. The most recent Cooperation Agreement was signed on 15 December 2010 with a term extending to 2020. For 2014, Canada’s annual assessed contribution to the ESA general budget was €6,059,449 (CAD$8,559,050). For 2017, Canada has increased its annual contribution to €21,600,000 (CAD$30,000,000).


    After the decision of the ESA Council of 21/22 March 2001, the procedure for accession of the European states was detailed as described the document titled The Plan for European Co-operating States (PECS). Nations that want to become a full member of ESA do so in 3 stages. First a Cooperation Agreement is signed between the country and ESA. In this stage, the country has very limited financial responsibilities. If a country wants to co-operate more fully with ESA, it signs a European Cooperating State (ECS) Agreement. The ECS Agreement makes companies based in the country eligible for participation in ESA procurements. The country can also participate in all ESA programmes, except for the Basic Technology Research Programme. While the financial contribution of the country concerned increases, it is still much lower than that of a full member state. The agreement is normally followed by a Plan For European Cooperating State (or PECS Charter). This is a 5-year programme of basic research and development activities aimed at improving the nation’s space industry capacity. At the end of the 5-year period, the country can either begin negotiations to become a full member state or an associated state or sign a new PECS Charter.

    During the Ministerial Meeting in December 2014, ESA ministers approved a resolution calling for discussions to begin with Israel, Australia and South Africa on future association agreements. The ministers noted that “concrete cooperation is at an advanced stage” with these nations and that “prospects for mutual benefits are existing”.

    A separate space exploration strategy resolution calls for further co-operation with the United States, Russia and China on “LEO exploration, including a continuation of ISS cooperation and the development of a robust plan for the coordinated use of space transportation vehicles and systems for exploration purposes, participation in robotic missions for the exploration of the Moon, the robotic exploration of Mars, leading to a broad Mars Sample Return mission in which Europe should be involved as a full partner, and human missions beyond LEO in the longer term.”

    Relationship with the European Union

    The political perspective of the European Union (EU) was to make ESA an agency of the EU by 2014, although this date was not met. The EU member states provide most of ESA’s funding, and they are all either full ESA members or observers.


    At the time ESA was formed, its main goals did not encompass human space flight; rather it considered itself to be primarily a scientific research organisation for uncrewed space exploration in contrast to its American and Soviet counterparts. It is therefore not surprising that the first non-Soviet European in space was not an ESA astronaut on a European space craft; it was Czechoslovak Vladimír Remek who in 1978 became the first non-Soviet or American in space (the first man in space being Yuri Gagarin of the Soviet Union) – on a Soviet Soyuz spacecraft, followed by the Pole Mirosław Hermaszewski and East German Sigmund Jähn in the same year. This Soviet co-operation programme, known as Intercosmos, primarily involved the participation of Eastern bloc countries. In 1982, however, Jean-Loup Chrétien became the first non-Communist Bloc astronaut on a flight to the Soviet Salyut 7 space station.

    Because Chrétien did not officially fly into space as an ESA astronaut, but rather as a member of the French CNES astronaut corps, the German Ulf Merbold is considered the first ESA astronaut to fly into space. He participated in the STS-9 Space Shuttle mission that included the first use of the European-built Spacelab in 1983. STS-9 marked the beginning of an extensive ESA/NASA joint partnership that included dozens of space flights of ESA astronauts in the following years. Some of these missions with Spacelab were fully funded and organizationally and scientifically controlled by ESA (such as two missions by Germany and one by Japan) with European astronauts as full crew members rather than guests on board. Beside paying for Spacelab flights and seats on the shuttles, ESA continued its human space flight co-operation with the Soviet Union and later Russia, including numerous visits to Mir.

    During the latter half of the 1980s, European human space flights changed from being the exception to routine and therefore, in 1990, the European Astronaut Centre in Cologne, Germany was established. It selects and trains prospective astronauts and is responsible for the co-ordination with international partners, especially with regard to the International Space Station. As of 2006, the ESA astronaut corps officially included twelve members, including nationals from most large European countries except the United Kingdom.

    In the summer of 2008, ESA started to recruit new astronauts so that final selection would be due in spring 2009. Almost 10,000 people registered as astronaut candidates before registration ended in June 2008. 8,413 fulfilled the initial application criteria. Of the applicants, 918 were chosen to take part in the first stage of psychological testing, which narrowed down the field to 192. After two-stage psychological tests and medical evaluation in early 2009, as well as formal interviews, six new members of the European Astronaut Corps were selected – five men and one woman.

    Cooperation with other countries and organisations

    ESA has signed co-operation agreements with the following states that currently neither plan to integrate as tightly with ESA institutions as Canada, nor envision future membership of ESA: Argentina, Brazil, China, India (for the Chandrayan mission), Russia and Turkey.

    Additionally, ESA has joint projects with the European Union, NASA of the United States and is participating in the International Space Station together with the United States (NASA), Russia and Japan (JAXA).

    European Union
    ESA and EU member states
    ESA-only members
    EU-only members

    ESA is not an agency or body of the European Union (EU), and has non-EU countries (Norway, Switzerland, and the United Kingdom) as members. There are however ties between the two, with various agreements in place and being worked on, to define the legal status of ESA with regard to the EU.

    There are common goals between ESA and the EU. ESA has an EU liaison office in Brussels. On certain projects, the EU and ESA co-operate, such as the upcoming Galileo satellite navigation system. Space policy has since December 2009 been an area for voting in the European Council. Under the European Space Policy of 2007, the EU, ESA and its Member States committed themselves to increasing co-ordination of their activities and programmes and to organising their respective roles relating to space.

    The Lisbon Treaty of 2009 reinforces the case for space in Europe and strengthens the role of ESA as an R&D space agency. Article 189 of the Treaty gives the EU a mandate to elaborate a European space policy and take related measures, and provides that the EU should establish appropriate relations with ESA.

    Former Italian astronaut Umberto Guidoni, during his tenure as a Member of the European Parliament from 2004 to 2009, stressed the importance of the European Union as a driving force for space exploration, “…since other players are coming up such as India and China it is becoming ever more important that Europeans can have an independent access to space. We have to invest more into space research and technology in order to have an industry capable of competing with other international players.”

    The first EU-ESA International Conference on Human Space Exploration took place in Prague on 22 and 23 October 2009. A road map which would lead to a common vision and strategic planning in the area of space exploration was discussed. Ministers from all 29 EU and ESA members as well as members of parliament were in attendance.

    National space organisations of member states:

    The Centre National d’Études Spatiales(FR) (CNES) (National Centre for Space Study) is the French government space agency (administratively, a “public establishment of industrial and commercial character”). Its headquarters are in central Paris. CNES is the main participant on the Ariane project. Indeed, CNES designed and tested all Ariane family rockets (mainly from its centre in Évry near Paris)
    The UK Space Agency is a partnership of the UK government departments which are active in space. Through the UK Space Agency, the partners provide delegates to represent the UK on the various ESA governing bodies. Each partner funds its own programme.
    The Italian Space Agency A.S.I. – Agenzia Spaziale Italiana was founded in 1988 to promote, co-ordinate and conduct space activities in Italy. Operating under the Ministry of the Universities and of Scientific and Technological Research, the agency cooperates with numerous entities active in space technology and with the president of the Council of Ministers. Internationally, the ASI provides Italy’s delegation to the Council of the European Space Agency and to its subordinate bodies.
    The German Aerospace Center (DLR)[Deutsches Zentrum für Luft- und Raumfahrt e. V.] is the national research centre for aviation and space flight of the Federal Republic of Germany and of other member states in the Helmholtz Association. Its extensive research and development projects are included in national and international cooperative programmes. In addition to its research projects, the centre is the assigned space agency of Germany bestowing headquarters of German space flight activities and its associates.
    The Instituto Nacional de Técnica Aeroespacial (INTA)(ES) (National Institute for Aerospace Technique) is a Public Research Organization specialised in aerospace research and technology development in Spain. Among other functions, it serves as a platform for space research and acts as a significant testing facility for the aeronautic and space sector in the country.


    ESA has a long history of collaboration with NASA. Since ESA’s astronaut corps was formed, the Space Shuttle has been the primary launch vehicle used by ESA’s astronauts to get into space through partnership programmes with NASA. In the 1980s and 1990s, the Spacelab programme was an ESA-NASA joint research programme that had ESA develop and manufacture orbital labs for the Space Shuttle for several flights on which ESA participate with astronauts in experiments.

    In robotic science mission and exploration missions, NASA has been ESA’s main partner. Cassini–Huygens was a joint NASA-ESA mission, along with the Infrared Space Observatory, INTEGRAL, SOHO, and others. Also, the Hubble Space Telescope is a joint project of NASA and ESA. Future ESA-NASA joint projects include the James Webb Space Telescope and the proposed Laser Interferometer Space Antenna. NASA has committed to provide support to ESA’s proposed MarcoPolo-R mission to return an asteroid sample to Earth for further analysis. NASA and ESA will also likely join together for a Mars Sample Return Mission. In October 2020 the ESA entered into a memorandum of understanding (MOU) with NASA to work together on the Artemis program, which will provide an orbiting lunar gateway and also accomplish the first manned lunar landing in 50 years, whose team will include the first woman on the Moon. Astronaut selection announcements are expected within two years of the 2024 scheduled launch date.

    Cooperation with other space agencies

    Since China has started to invest more money into space activities, the Chinese Space Agency(CN) has sought international partnerships. ESA is, beside the Russian Space Agency, one of its most important partners. Two space agencies cooperated in the development of the Double Star Mission. In 2017, ESA sent two astronauts to China for two weeks sea survival training with Chinese astronauts in Yantai, Shandong.

    ESA entered into a major joint venture with Russia in the form of the CSTS, the preparation of French Guiana spaceport for launches of Soyuz-2 rockets and other projects. With India, ESA agreed to send instruments into space aboard the ISRO’s Chandrayaan-1 in 2008. ESA is also co-operating with Japan, the most notable current project in collaboration with JAXA is the BepiColombo mission to Mercury.

    Speaking to reporters at an air show near Moscow in August 2011, ESA head Jean-Jacques Dordain said ESA and Russia’s Roskosmos space agency would “carry out the first flight to Mars together.”

  • richardmitnick 4:05 pm on January 3, 2021 Permalink | Reply
    Tags: "The Milky Way Gets a New Origin Story", , , , , Gaia EDR3,   

    From WIRED: “The Milky Way Gets a New Origin Story” 

    From WIRED

    Charlie Wood

    A large Milky Way–like galaxy collides with a smaller dwarf galaxy in this digital simulation. Astronomers believe that at least one major collision like this happened early in the Milky Way’s development.

    A large Milky Way-like galaxy collides with a smaller dwarf galaxy in this digital simulation. Astronomers believe that at least one major collision like this happened early in the Milky Way’s development.Credit: VIDEO: KOPPELMAN, VILLALOBOS & HELMI.

    When the Khoisan hunter-gatherers of sub-Saharan Africa gazed upon the meandering trail of stars and dust that split the night sky, they saw the embers of a campfire. Polynesian sailors perceived a cloud-eating shark. The ancient Greeks saw a stream of milk, gala, which would eventually give rise to the modern term “galaxy.”

    In the 20th century, astronomers discovered that our silver river is just one piece of a vast island of stars, and they penned their own galactic origin story. In the simplest telling, it held that our Milky Way galaxy came together nearly 14 billion years ago when enormous clouds of gas and dust coalesced under the force of gravity. Over time, two structures emerged: first, a vast spherical “halo,” and later, a dense, bright disk. Billions of years after that, our own solar system spun into being inside this disk, so that when we look out at night, we see spilt milk—an edge-on view of the disk splashed across the sky.

    Yet over the past two years, researchers have rewritten nearly every major chapter of the galaxy’s history. What happened? They got better data.

    On April 25, 2018, a European spacecraft by the name of Gaia released a staggering quantity of information about the sky.

    ESA (EU)/GAIA satellite .

    Critically, Gaia’s years-long data set described the detailed motions of roughly 1 billion stars. Previous surveys had mapped the movement of just thousands. The data brought a previously static swath of the galaxy to life. “Gaia started a new revolution,” said Federico Sestito, an astronomer at the Strasbourg Astronomical Observatory in France.

    Gaia EDR3 StarTrails 600.

    The river of stars in the southern sky. ESA/GAIA (Gaia DR2 skymap)

    Data from more than 1.8 billion stars have been used to create this map of the entire sky. It shows the total brightness and color of stars observed by ESA’s Gaia satellite and released as part of Gaia’s Early Data Release 3.

    Astronomers raced to download the dynamic star map, and a flurry of discoveries followed. They found that parts of the disk, for example, appeared impossibly ancient. They also found evidence of epic collisions that shaped the Milky Way’s violent youth, as well as new signs that the galaxy continues to churn in an unexpected way.

    The Gaia satellite has revolutionized our understanding of the Milky Way since its launch in December 2013. Credit:Video from ESA/ATG Media Lab.

    Taken together, these results have spun a new story about our galaxy’s turbulent past and its ever-evolving future. “Our picture of the Milky Way has changed so quickly,” said Michael Petersen, an astronomer at the University of Edinburgh. “The theme is that the Milky Way is not a static object. Things are changing rapidly everywhere.”

    The Earliest Stars

    To peer back to the galaxy’s earliest days, astronomers seek stars that were around back then. These stars were fashioned only from hydrogen and helium, the cosmos’s rawest materials. Fortunately, the smaller stars from this early stock are also slow to burn, so many are still shining.

    After decades of surveys, researchers had assembled a catalog of 42 such ancients, known as ultra metal-poor stars (to astronomers, any atom bulkier than helium qualifies as metallic). According to the standard story of the Milky Way, these stars should be swarming throughout the halo, the first part of the galaxy to form. By contrast, stars in the disk—which was thought to have taken perhaps an additional billion years to spin itself flat—should be contaminated with heaver elements such as carbon and oxygen.

    In late 2017, Sestito set out to study how this metal-poor swarm moves by writing code to analyze the upcoming Gaia results. Perhaps their spherical paths could offer some clues as to how the halo came to be, he thought.

    In the days following Gaia’s data release, he extracted the 42 ancient stars from the full data set, then tracked their motions. He found that most were streaming through the halo, as predicted. But some—roughly 1 in 4—weren’t. Rather, they appeared stuck in the disk [MNRAS], the Milky Way’s youngest region. “What the hell,” Sestito wondered, though he used a different four-letter term. “What’s going on?”

    Follow-up research confirmed that the stars really are long-term residents of the disk, and not just tourists passing through. From two recent surveys, Sestito and colleagues amassed a library of roughly 5,000 metal-poor stars. A few hundred of them appear to be permanent denizens of the disk [MNRAS]. Another group sifted through about 500 stars identified by another survey, finding that about 1 in 10 of these stars lie flat in circular, sunlike orbits [MNRAS]. And a third research group found stars of various metallicities (and therefore various ages) moving in flat disk orbits. “This is something completely new,” said lead author Paola Di Matteo, an astronomer at the Paris Observatory.

    How did these anachronisms get there? Sestito speculated that perhaps pockets of pristine gas managed to dodge all the metals expelled from supernovas for eons, then collapsed to form stars that looked deceptively old. Or the disk may have started taking shape when the halo did, nearly 1 billion years ahead of schedule.

    To see which was more probable, he connected with Tobias Buck, a researcher at the Leibniz Institute for Astrophysics in Potsdam, Germany, who specializes in crafting digital galaxy simulations. Past efforts had generally produced halos first and disks second, as expected. But these were relatively low-resolution efforts.

    Galaxy simulation
    In these digital simulations, a Milky Way–like galaxy forms and evolves over 13.8 billion years — from the early universe to the present day. The leftmost column shows the distribution of invisible dark matter; the center column the temperature of gas (where blue is cold and red is hot); and the right column the density of stars. Each row highlights a different size scale: The top row is a zoomed-in look at the galactic disk; the center column a mid-range view of the galactic halo; and the bottom row a zoomed-out view of the environment around the galaxy.

    Buck increased the crispness of his simulations by about a factor of 10. At that resolution, each run demanded intensive computational resources. Even though he had access to Germany’s Leibniz Supercomputing Center, a single simulation required three months of computing time. He repeated the exercise six times.

    Of those six, five produced Milky Way doppelgängers. Two of those featured substantial numbers of metal-poor disk stars.

    How did those ancient stars get into the disk? Simply put, they were stellar immigrants. Some of them were born in clouds that predated the Milky Way. Then the clouds just happened to deposit some of their stars into orbits that would eventually form part of the galactic disk. Other stars came from small “dwarf” galaxies that slammed into the Milky Way and aligned with an emerging disk.

    The results, which the group published in November [MNRAS], suggest that the classic galaxy formation models were incomplete. Gas clouds do collapse into spherical halos, as expected. But stars arriving at just the right angles can kick-start a disk at the same time. “[Theorists] weren’t wrong,” Buck said. “They were missing part of the picture.”

    A Violent Youth

    The complications don’t end there. With Gaia, astronomers have found direct evidence of cataclysmic collisions. Astronomers assumed that the Milky Way had a hectic youth, but Helmer Koppelman, an astronomer now at the Institute for Advanced Study in Princeton, New Jersey, used the Gaia data to help pinpoint specific debris from one of the largest mergers.

    Gaia’s 2018 data release fell on a Wednesday, and the mad rush to download the catalog froze its website, Koppelman recalled. He processed the data on Thursday, and by Friday he knew he was on to something big. In every direction, he saw a huge number of halo stars ping-ponging back and forth in the center of the Milky Way in the same peculiar way—a clue that they had come from a single dwarf galaxy. Koppelman and his colleagues had a brief paper [The Astrophysical Journal Letters] ready by Sunday and followed it up with a more detailed analysis that June [Nature].

    The galactic wreckage was everywhere. Perhaps half of all the stars in the inner 60,000 light-years of the halo (which extends hundreds of thousands of light-years in every direction) came from this lone collision, which may have boosted the young Milky Way’s mass by as much as 10 percent. “This is a game changer for me,” Koppelman said. “I expected many different smaller objects.”

    A simulation shows the formation and evolution of a Milky Way–like galaxy over about 10 billion years. Many smaller dwarf galaxies accrete onto the main galaxy, often becoming a part of it.Video credit: Tobias Buck.

    The group named the incoming galaxy Gaia-Enceladus, after the Greek goddess Gaia—one of the primordial deities—and her Titan son Enceladus. Another team at the University of Cambridge independently discovered the galaxy around the same time [MNRAS], dubbing it the Sausage for its appearance in certain orbital charts.

    When the Milky Way and Gaia-Enceladus collided, perhaps 10 billion years ago, the Milky Way’s delicate disk may have suffered widespread damage. Astronomers debate why our galactic disk seems to have two parts: a thin disk, and a thicker one where stars bungee up and down while orbiting the galactic center. Research led by Di Matteo[Astronomy & Astrophysics] now suggests that Gaia-Enceladus exploded much of the disk, puffing it up during the collision. “The first ancient disk formed pretty fast, and then we think Gaia-Enceladus kind of destroyed it,” Koppelman said.

    Hints of additional mergers have been spotted in bundles of stars known as globular clusters. Diederik Kruijssen, an astronomer at Heidelberg University in Germany, used galaxy simulations to train a neural network to scrutinize globular clusters. He had it study their ages, makeup, and orbits. From that data, the neural network could reconstruct the collisions that assembled the galaxies. Then he set it loose on data from the real Milky Way. The program reconstructed known events such as Gaia-Enceladus, as well as an older, more significant merger that the group has dubbed Kraken.

    In August, Kruijssen’s group published a merger lineage of the Milky Way and the dwarf galaxies that formed it [MNRAS]. They also predicted the existence of 10 additional past collisions that they’re hoping will be confirmed with independent observations. “We haven’t found the other 10 yet,” Kruijssen said, “but we will.”

    All these mergers have led some astronomers to suggest [The Astrophysical Journal] that the halo may be made almost exclusively of immigrant stars. Models from the 1960s and ’70s predicted that most Milky Way halo stars should have formed in place. But as more and more stars have been identified as galactic interlopers, astronomers may not need to assume that many, if any, stars are natives, said Di Matteo.

    A Still-Growing Galaxy

    The Milky Way has enjoyed a relatively quiet history in recent eons, but newcomers continue to stream in. Stargazers in the Southern Hemisphere can spot with the naked eye a pair of dwarf galaxies called the Large and Small Magellanic Clouds. Astronomers long believed the pair to be our steadfast orbiting companions, like moons of the Milky Way.

    Then a series of Hubble Space Telescope observations [The Astrophysical Journal] between 2006 and 2013 found that they were more like incoming meteorites. Nitya Kallivayalil, an astronomer at the University of Virginia, clocked the clouds as coming in hot at about 330 kilometers per second—nearly twice as fast as had been predicted.

    When a team led by Jorge Peñarrubia, an astronomer at the Royal Observatory of Edinburgh, crunched the numbers a few years later, they concluded that the speedy clouds must be extremely hefty—perhaps 10 times bulkier than previously thought.

    “It’s been surprise after surprise,” Peñarrubia said.

    Various groups have predicted that the unexpectedly beefy dwarfs might be dragging parts of the Milky Way around, and this year Peñarrubia teamed up with Petersen to find proof.

    The problem with looking for galaxy-wide motion is that the Milky Way is a raging blizzard of stars, with astronomers looking outward from one of the snowflakes. So Peñarrubia and Petersen spent most of lockdown figuring out how to neutralize the motions of the Earth and the sun, and how to average out the motion of halo stars so that the halo’s outer fringe could serve as a stationary backdrop.

    When they calibrated the data in this way, they found that the Earth, the sun, and the rest of the disk in which they sit are lurching in one direction—not toward the Large Magellanic Cloud’s current position, but toward its position around a billion years ago (the galaxy is a lumbering beast with slow reflexes, Petersen explained). They recently detailed their findings in Nature Astronomy.

    The sliding of the disk against the halo undermines a fundamental assumption: that the Milky Way is an object in balance. It may spin and slip through space, but most astronomers assumed that after billions of years, the mature disk and the halo had settled into a stable configuration.

    Peñarrubia and Petersen’s analysis proves that assumption wrong. Even after 14 billion years, mergers continue to sculpt the overall shape of the galaxy. This realization is just the latest change in how we understand the great stream of milk across the sky.

    “Everything we thought we knew about the future and the history of the Milky Way,” said Petersen, “we need a new model to describe that.”

    See the full article here .


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  • richardmitnick 12:57 pm on December 3, 2020 Permalink | Reply
    Tags: "Gaia's new data takes us to the Milky Way's anticentre and beyond", , , , , , Gaia EDR3   

    From European Space Agency – United Space in Europe (EU): “Gaia’s new data takes us to the Milky Way’s anticentre and beyond” 

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    From European Space Agency – United Space in Europe (EU)

    3 December 2020

    The motion of stars in the outskirts of our galaxy hints at significant changes in the history of the Milky Way. This and other equally fascinating results come from a set of papers that demonstrate the quality of ESA’s Gaia Early third Data Release (EDR3), which is made public today.

    Gaia’s stellar motion for the next 400 thousand years. Credit: ESA/Gaia/DPAC, CC BY-SA 3.0 IGO. Acknowledgement: A. Brown, S. Jordan, T. Roegiers, X. Luria, E. Masana, T. Prusti and A. Moitinho.

    Astronomers from the Gaia Data Processing and Analysis Consortium (DPAC) saw the evidence of the Milky Way’s past by looking at stars in the direction of the galaxy’s ‘anticentre’. This is in the exact opposite direction on the sky from the centre of the galaxy.

    The results on the anticentre come from one of the four ‘demonstration papers’ released alongside the Gaia data. The others use Gaia data to provide a huge extension to the census of nearby stars, derive the shape of the Solar System’s orbit around the centre of the galaxy, and probe structures in two nearby galaxies to the Milky Way. The papers are designed to highlight the improvements and quality of the newly published data.

    What’s new in EDR3?

    Gaia EDR3 contains detailed information on more than 1.8 billion sources, detected by the Gaia spacecraft. This represents an increase of more than 100 million sources over the previous data release (Gaia DR2), which was made public in April 2018.

    The colour of the sky from Gaia’s Early Data Release 3. Credit: ESA/Gaia/DPAC; CC BY-SA 3.0 IGO. Acknowledgement: A. Moitinho.

    Gaia EDR3 also contains colour information for around 1.5 billion sources, an increase of about 200 million sources over Gaia DR2. As well as including more sources, the general accuracy and precision of the measurements has also improved.

    “The new Gaia data promise to be a treasure trove for astronomers,” says Jos de Bruijne, ESA’s Gaia Deputy Project Scientist.

    To the galactic anticentre

    The new Gaia data have allowed astronomers to trace the various populations of older and younger stars out towards the very edge of our galaxy – the galactic anticentre. Computer models predicted that the disc of the Milky Way will grow larger with time as new stars are born. The new data allow us to see the relics of the 10 billion-year-old ancient disc and so determine its smaller extent compared to the Milky Way’s current disc size.

    The new data from these outer regions also strengthen the evidence for another major event in the more recent past of the galaxy.

    The data show that in the outer regions of the disc there is a component of slow-moving stars above the plane of our galaxy that are heading downwards towards the plane, and a component of fast-moving stars below the plane that are moving upwards. This extraordinary pattern had not been anticipated before. It could be the result of the near-collision between the Milky Way and the Sagittarius dwarf galaxy that took place in our galaxy’s more recent past.

    The Sagittarius dwarf galaxy contains a few tens of millions of stars and is currently in the process of being cannibalised by the Milky Way. Its last close pass to our galaxy was not a direct hit, but this would have been enough so that its gravity perturbed some stars in our galaxy like a stone dropping into water.

    Using Gaia DR2, members of DPAC had already found a subtle ripple in the movement of millions of stars that suggested the effects of the encounter with Sagittarius sometime between 300 and 900 million years ago. Now, using Gaia EDR3, they have uncovered more evidence that points to its strong effects on our galaxy’s disc of stars.

    “The patterns of movement in the disc stars are different to what we used to believe,” says Teresa Antoja, University of Barcelona, Spain, who worked on this analysis with DPAC colleagues. Although the role of the Sagittarius dwarf galaxy is still debated in some quarters, Teresa says, “It could be a good candidate for all these disturbances, as some simulations from other authors show.”

    Measuring the Solar System’s orbit

    The history of the galaxy is not the only result from the Gaia EDR3 demonstration papers. DPAC members across Europe have performed other work to demonstrate the extreme fidelity of the data and the unique potential for unlimited scientific discovery.

    In one paper, Gaia has allowed scientists to measure the acceleration of the Solar System with respect to the rest frame of the Universe. Using the observed motions of extremely distant galaxies, the velocity of the Solar System has been measured to change by 0.23 nm/s every second. Because of this tiny acceleration the trajectory of the Solar System is deflected by the diameter of an atom every second, and in a year this adds up to around 115 km. The acceleration measured by Gaia shows a good agreement with the theoretical expectations and provides the first measurement of the curvature of the Solar System’s orbit around the galaxy in the history of optical astronomy.

    A new stellar census

    Gaia EDR3 has also allowed a new census of stars in the solar neighbourhood to be obtained. The Gaia Catalogue of Nearby Stars contains 331 312 objects, which is estimated to be 92 percent of the stars within 100 parsecs (326 light years) of the Sun. The previous census of the solar neighbourhood, called the Gliese Catalogue of Nearby stars, was carried out in 1957. It possessed just 915 objects initially, but was updated in 1991 to 3803 celestial objects. It was also limited to a distance of 82 light years: Gaia’s census reaches four times farther and contains 100 times more stars. It also provides location, motion, and brightness measurements that are orders of magnitude more precise than the old data.

    Beyond the Milky Way

    A fourth demonstration paper analysed the Magellanic Clouds: two galaxies that orbit the Milky Way. Having measured the movement of the Large Magellanic Cloud’s stars to greater precision than before, Gaia EDR3 clearly shows that the galaxy has a spiral structure. The data also resolve a stream of stars that is being pulled out of the Small Magellanic Cloud, and hints at previously unseen structures in the outskirts of both galaxies.

    At 12:00 CET on 3 December, the data produced by the many scientists and engineers of the Gaia DPAC Consortium become public for anyone to look at and learn from. This is the first of a two-part release; the full Data Release 3 is planned for 2022.

    “Gaia EDR3 is the result of a huge effort from everyone involved in the Gaia mission. It’s an extraordinarily rich data set, and I look forward to the many discoveries that astronomers from around the world will make with this resource,” says Timo Prusti, ESA’s Gaia Project Scientist. “And we’re not done yet; more great data will follow as Gaia continues to make measurements from orbit.”

    Astronomy & Astrophysics
    Gaia Early Data Release 3
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    Free Access
    Gaia Early Data Release 3: The Gaia Catalogue of Nearby Stars
    R.L. Smart, L. M. Sarro, J. Rybizki, et al.
    Received: 22 September 2020 / Accepted: 30 October 2020
    DOI: https://doi.org/10.1051/0004-6361/202039498

    PDF (7.131 MB)

    Free Access
    Gaia Early Data Release 3: Photometric content and validation
    M. Riello, F. De Angeli, D. W. Evans, et al.
    Received: 03 October 2020 / Accepted: 24 November 2020
    DOI: https://doi.org/10.1051/0004-6361/202039587

    PDF (19.89 MB)

    Free Access
    Gaia Early Data Release 3: Structure and properties of the Magellanic Clouds
    Gaia Collaboration, X. Luri, L. Chemin, G. Clementini, H.E. Delgado, P.J. McMillan, M. Romero-Gómez, E. Balbinot, A. Castro-Ginard, R. Mor, V. Ripepi, L.M. Sarro, M.-R. L. Cioni, C. Fabricius, A. Garofalo, A. Helmi, T. Muraveva et al.
    Received: 03 October 2020 / Accepted: 22 November 2020
    DOI: https://doi.org/10.1051/0004-6361/202039588

    PDF (37.20 MB)

    Free Access
    Gaia Early Data Release 3. Building the Gaia DR3 source list – Cross-match of Gaia observations
    F. Torra, J. Castañeda, C. Fabricius, L. Lindegren, M. Clotet, J.J. González-Vidal, S. Bartolomé, U. Bastian, M. Bernet, M. Biermann, N. Garralda, A. Gúrpide, U. Lammers, J. Portell, J. Torra
    Received: 09 October 2020 / Accepted: 21 November 2020
    DOI: https://doi.org/10.1051/0004-6361/202039637

    PDF (17.89 MB)

    Free Access
    Gaia Early Data Release 3. Summary of the contents and survey properties
    Gaia Collaboration, A. G. A. Brown, A. Vallenari, T. Prusti, J.H.J. de Bruijne, et al.
    Received: 12 October 2020 / Accepted: 29 October 2020
    DOI: https://doi.org/10.1051/0004-6361/202039657

    PDF (558.0 KB)

    Free Access
    Gaia Early Data Release 3. The astrometric solution
    L. Lindegren, S.A. Klioner, J. Hernández, A. Bombrun, M. Ramos-Lerate, H. Steidelmüller, U. Bastian, M. Biermann, A. de Torres, E. Gerlach, R. Geyer, T. Hilger, D. Hobbs, U. Lammers, P.J. McMillan, C.A. Stephenson, J. Castañeda, M. Davidson, et al.
    Received: 18 October 2020 / Accepted: 18 November 2020
    DOI: https://doi.org/10.1051/0004-6361/202039709

    PDF (11.79 MB)

    Free Access
    Gaia Early Data Release 3 – Catalogue validation
    Received: 03 November 2020 / Accepted: 27 November 2020
    DOI: https://doi.org/10.1051/0004-6361/202039834

    PDF (7.876 MB)

    See the full article here .

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    The European Space Agency (ESA) (EU), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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