ESA Gaia Spacecraft

Flyaway

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Astronomers at Harvard University have discovered a monolithic, wave-shaped gaseous structure—the largest ever seen in our galaxy—made up of interconnected stellar nurseries. Dubbed the "Radcliffe wave" in honor of the collaboration's home base, the Radcliffe Institute for Advanced Study, the discovery transforms a 150-year-old vision of nearby stellar nurseries as an expanding ring into one featuring an undulating, star-forming filament that reaches trillions of miles above and below the galactic disk.

The work, published in Nature on 7 January, was enabled by a new analysis of data from the European Space Agency's Gaia spacecraft, launched in 2013 with the mission of precisely measuring the position, distance, and motion of the stars. The research team combined the super-accurate data from Gaia with other measurements to construct a detailed, 3-D map of interstellar matter in the Milky Way, and noticed an unexpected pattern in the spiral arm closest to the Earth.

"We don't know what causes this shape but it could be like a ripple in a pond, as if something extraordinarily massive landed in our galaxy," said Alves. "What we do know is that our Sun interacts with this structure. It passed by a festival of supernovae as it crossed Orion 13 million years ago, and in another 13 million years it will cross the structure again, sort of like we are 'surfing the wave'."


Here’s the related paper:

 

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Gaia revolutionises asteroid tracking

01/07/2020

ESA’s Gaia space observatory is an ambitious mission to construct a three-dimensional map of our galaxy by making high-precision measurements of over one billion stars. However, on its journey to map distant suns, Gaia is revolutionising a field much closer to home. By accurately mapping the stars, it is helping researchers track down lost asteroids.

 

Flyaway

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So Caballero repeated the search, looking for Sun-like stars among the thousands that have been identified by Gaia in this region of the sky. By Sun-like, he means stars that share the same temperature, radius and luminosity
.

The search returned just one candidate. “The only potential Sun-like star in all the WOW! Signal region appears to be 2MASS 19281982-2640123,” says Caballero. This star sits in the constellation of Sagittarius at a distance of 1800 light-years. It is an identical twin to our Sun, with the same temperature, radius, and luminosity.

Of course, Caballero’s work does not mean that 2MASS 19281982-2640123 must have been the source. He points out that there are many stars in that region of the sky that are too dim to be included in the catalog. One of these could be the source.



An approximation to determine the source of the WOW! Signal

In this paper it is analysed which of the thousands of stars in the WOW! Signal region could have the highest chance of being the real source of the signal, providing that it came from a star system similar to ours. A total of 66 G and K-type stars are sampled, but only one of them is identified as a potential Sun-like star considering the available information in the Gaia Archive. This candidate source, which is named 2MASS 19281982-2640123, therefore becomes an ideal target to conduct observations in the search for potentially habitable exoplanets. Another 14 potential Sun-like stars (with estimated temperatures between 5,730 and 5,830 K) are also found in the region, but information about their luminosity and radius is unknown.

 

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So Caballero repeated the search, looking for Sun-like stars among the thousands that have been identified by Gaia in this region of the sky. By Sun-like, he means stars that share the same temperature, radius and luminosity
.

The search returned just one candidate. “The only potential Sun-like star in all the WOW! Signal region appears to be 2MASS 19281982-2640123,” says Caballero. This star sits in the constellation of Sagittarius at a distance of 1800 light-years. It is an identical twin to our Sun, with the same temperature, radius, and luminosity.

Of course, Caballero’s work does not mean that 2MASS 19281982-2640123 must have been the source. He points out that there are many stars in that region of the sky that are too dim to be included in the catalog. One of these could be the source.



An approximation to determine the source of the WOW! Signal

In this paper it is analysed which of the thousands of stars in the WOW! Signal region could have the highest chance of being the real source of the signal, providing that it came from a star system similar to ours. A total of 66 G and K-type stars are sampled, but only one of them is identified as a potential Sun-like star considering the available information in the Gaia Archive. This candidate source, which is named 2MASS 19281982-2640123, therefore becomes an ideal target to conduct observations in the search for potentially habitable exoplanets. Another 14 potential Sun-like stars (with estimated temperatures between 5,730 and 5,830 K) are also found in the region, but information about their luminosity and radius is unknown.


An interesting discovery about the Wow signal. I wonder wonder if they could point the planet finding telescopes at the star to see if they can detect the source planet?
 

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There Should be About 7 Interstellar Objects Passing Through the Inner Solar System Every Year.

Interstellar Objects in the Solar System: 1. Isotropic Kinematics from the Gaia Early Data Release 3

1I/'Oumuamua (or 1I) and 2I/Borisov (or 2I), the first InterStellar Objects (ISOs) discovered passing through the solar system, have opened up entirely new areas of exobody research. Finding additional ISOs and planning missions to intercept or rendezvous with these bodies will greatly benefit from knowledge of their likely orbits and arrival rates. Here, we use the local velocity distribution of stars from the Gaia Early Data Release 3 Catalogue of Nearby Stars and a standard gravitational focusing model to predict the velocity dependent flux of ISOs entering the solar system. With an 1I-type ISO number density of ∼0.1 AU−3, we predict that a total of ∼6.9 such objects per year should pass within 1 AU of the Sun. There will be a fairly large high-velocity tail to this flux, with half of the incoming ISOs predicted to have a velocity at infinity, v∞, > 40 km s−1. Our model predicts that ∼92\% of incoming ISOs will be residents of the galactic thin disk, ∼6\% (∼4 per decade) will be from the thick disk, ∼1 per decade will be from the halo and at most ∼3 per century will be unbound objects, ejected from our galaxy or entering the Milky Way from another galaxy. The rate of ISOs with very low v∞ ≲ 1.5 km s−1 is so low in our model that any incoming very low velocity ISOs are likely to be previously lost solar system objects. Finally, we estimate a cometary ISO number density of ∼7 × 10−5 AU−3 for 2I type ISOs, leading to discovery rates for these objects possibly approaching once per decade with future telescopic surveys.


 

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Eh. PANSTAARS was supposed to pick up interstellar interlopers at a rate of one a year, according to the original paper.

Didn't really pan out.
 

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Eh. PANSTAARS was supposed to pick up interstellar interlopers at a rate of one a year, according to the original paper.

Didn't really pan out.
Interstellar objects have the advantage of near-perfect stealth; they are very cold, long ago emitting all residual heat they might have, and could came at literally any angle.
 

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Thanks to ESA's star mapping spacecraft Gaia and machine learning, astronomers have discovered 12 quasars whose light is so strongly deflected by foreground galaxies that they are each visible as four distinct images, called an 'Einstein cross'. These crosses are unique tools to learn more about dark matter and the expansion rate of the Universe.

 

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Gaia reveals that most Milky Way companion galaxies are newcomers to our corner of space

Data from ESA’s Gaia mission is re-writing the history of our galaxy, the Milky Way. What had traditionally been thought of as satellite galaxies to the Milky Way are now revealed to be mostly newcomers to our galactic environment.

A dwarf galaxy is a collection of between thousand and several billion stars. For decades it has been widely believed that the dwarf galaxies that surround the Milky Way are satellites, meaning that they are caught in orbit around our galaxy, and have been our constant companions for many billions of years. Now the motions of these dwarf galaxies have been computed with unprecedented precision thanks to data from Gaia’s early third data release and the results are surprising.

François Hammer, Observatoire de Paris - Université Paris Sciences et Lettres, France, and colleagues from across Europe and China, used the Gaia data to calculate the movements of 40 dwarf galaxies around the Milky Way. They did this by computing a set of quantities known as the three-dimensional velocities for each galaxy, and then using those to calculate the galaxy’s orbital energy and the angular (rotational) momentum.

They found that these galaxies are moving much faster than the giant stars and star clusters that are known to be orbiting the Milky Way. So fast, that they couldn’t be in orbit yet around the Milky Way, where interactions with our galaxy and its contents would have sapped their orbital energy and angular momentum.
 

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Gaia reveals a new member of the Milky Way family

Our galaxy, the Milky Way, began forming around 12 billion years ago. Since then, it has been growing in both mass and size through a sequence of mergers with other galaxies.

Perhaps most exciting is that this process has not quite finished, and by using data from ESA’s Gaia spacecraft, astronomers can see it taking place. This in turn allows to reconstruct the history of our galaxy, revealing the ‘family tree’ of smaller galaxies that has helped make the Milky Way what it is today.

The latest work on this subject comes from Khyati Malhan, a Humboldt Fellow at the Max-Planck-Institut für Astronomie, Heidelberg, Germany, and colleagues. Together, they have analysed data based on Gaia’s early third data release (EDR3) looking for the remains of smaller galaxies merging with our own. These can be found in the so-called halo of the Milky Way, which surrounds the disc of younger stars and central bulge of older stars that comprise the more luminous parts of the Milky Way.

In total they studied 170 globular clusters, 41 stellar streams and 46 satellites of the Milky Way. Plotting them according to their energy and momentum revealed that 25 percent of these objects fall into six distinct groups. Each group is a merger taking place with the Milky Way. There was also a possible seventh merger in the data.

Five had been previously identified on surveys of stars. They are known as Sagittarius, Cetus, Gaia-Sausage/Enceladus, LMS-1/Wukong, and Arjuna/Sequoia/I’itoi. But the sixth was a newly identified merger event. The team called it Pontus, meaning the sea. In Greek mythology, Pontus is the name of one of the first children of Gaia, the Greek goddess of the Earth.

Based upon the way Pontus has been pulled apart by the Milky Way, Khyati and colleagues estimate that it probably fell into the Milky Way some eight to ten billion years ago. Four of the other five merger events likely also took place around this time as well. But the sixth event, Sagittarius, is more recent. It might have fallen into the Milky Way sometime in the last five to six billion years. As a result, the Milky Way has not yet been able to completely disrupt it.

Piece by piece, astronomers are fitting together the merger history of the Galaxy, and Gaia data is proving invaluable.

On 13 June 2022, the Gaia mission will issue its data release 3, which will provide even more detailed information about the Milky Way’s past, present, and future.

Image description:

This image shows the Milky Way as seen by Gaia. The squares represent the location of globular clusters, the triangles the location of satellite galaxies, and the small dots are stellar streams. The dots and squares in purple are objects brought into the Milky Way by the Pontus merging galaxy.

This research by Khyati Malhan was published in The Astrophysical Journal. DOI: https://iopscience.iop.org/article/10.3847/1538-4357/ac4d2a

 

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CEPHEIDS AND THEIR RADIAL VELOCITY CURVES

The variable stars that nowadays are collectively called Cepheids are actually an ensemble of different types identifying three main groups: Classical Cepheids, type II Cepheids and anomalous Cepheids. Classical Cepheids are fundamental standard candles of the extragalactic distance scale. They are also important tracers of the young (~50-500 Myr) population in the host galaxy, while anomalous and type II Cepheids are believed to belong to the intermediate-age (few Gyr) and old (>10 Gyr) populations, respectively.

Gaia Data Release 3 (Gaia DR3) will release multi-band light-curves for more than 15,000 Cepheids of all types in five different environments, namely, the Large and Small Magellanic Clouds, the Andromeda (M31) and Triangulum (M33) galaxies and the Milky Way (including its cluster population and its small satellite dwarf galaxies).

These pulsating stars have been confirmed and fully characterised by the Specific Object Study pipeline for Cepheids and RR Lyrae stars (called SOS Cep&RRL, Clementini et al. 2016) developed by Coordination Unit 7 (CU7; variability processing) of the Gaia Data Processing and Analysis Consortium. Periods, amplitudes of the GBP, G and GRP light variations, and mean magnitudes computed as an intensity-average over the full pulsation cycle, will be published for these Cepheids, along with the parameters resulting from the Fourier decomposition of their G-band light curves (φ21, φ31, R21 and R31; see e.g. Clementini et al. 2016).

In addition, radial velocity time-series data will be released in Gaia DR3 for a subsample of about 800 Cepheids (see Ripepi et al. 2022, the paper describing the specific processing and validation of all-sky Cepheid variables released in Gaia DR3, for full details).

The light and radial velocity curves for a sample of classical Cepheids in the period range from ~7 to ~13 days are shown in Figure 1. The extraordinary precision of the Gaia data (uncertainties on the individual measurements are comparable with the symbol sizes) allows us to appreciate the “Hertzsprung Progression”, discovered about one century ago by the Danish astronomer E. Hertzsprung. This feature consists in the observation of a “bump” both in the light and radial velocity curves of classical Cepheids in the period range of 6 - 15 days, whose position moves from the descending to the rising branch of the light curve as the period increases. The “bump” is clearly discernible in the descending branch of the Cepheid BM Pup (P~7.2 days, top left in Figure 1); it moves backwards in phase becoming almost equivalent in magnitude to the main maximum for P~8.2 days, reaching the bottom of the ascending branch for V1364 Cyg (P~13 days, bottom right). The physical origin of the bump is not yet completely understood, however it is believed to be due to the resonance between the second overtone and the fundamental modes and it takes place when the period ratio between these two modes is close to 0.5.

The evolution of the bump phase as the period increases is observed and predicted from theoretical pulsation models to depend on the metallicity of the host galaxy. Indeed both models and observations point towards a longer period for the centre of the Hertzsprung Progression (the point where the bump reaches the same magnitude as the maximum light, immediately before it re-appears on the rising branch) as the metallicity of the host population decreases. Recent model predictions also suggest a dependence on the Helium abundance and the mass-luminosity relation. The position in period of the centre of the Hertzsprung Progression, accurately determined from Gaia light and radial velocity curves, can thus provide crucial constraints not only on the chemical composition of the observed classical Cepheids but also on the physics of intermediate mass stars.



References

Clementini et al. 2016: “Gaia Data Release 1. The Cepheid and RR Lyrae star pipeline and its application to the south ecliptic pole region”, A&A, 595, A133
Ripepi et al. 2022: “Gaia DR3: Specific processing and validation of all-sky RR Lyrae and Cepheid stars - The Cepheid sample”, A&A, submitted


Credits: ESA/Gaia/DPAC/CU7/CU6/CU5/INAF, Vincenzo Ripepi, Marcella Marconi, Roberto Molinaro, Silvio Leccia, Ilaria Musella (INAF-OACn Naples), Gisella Clementini, Alessia Garofalo (INAF-OAS Bologna), Laurent Eyer (University of Geneva) and the CU7/DPCG, CU5, and CU6 teams.

[Published: 27/05/2022]

 

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