Image of the Week

Close stellar encounters from the first Gaia data release

Figure 1: The open circles show the time (horizontal axis) and distance (vertical axis) of the closest approach of stars to the Sun. Negative times indicate times in the past from today. Each point has been calculated as the median of the distribution of a swarm of surrogate particles which have been integrated through a Galactic potential. The "error" bars show the limits of the 5% and 95% percentiles of these distributions (which together form an asymmetric 90% confidence interval). That is, the swarm is used to propagate the uncertainties in the TGAS measurements to uncertainties in the perihelion parameters. The background colour (scale on the right) indicates the estimated completeness of the TGAS survey. That is, if all TGAS stars had radial velocities (and most do not), this gives the probability that a star with any particular perihelion parameters would be present in TGAS. Image credit: Coryn Bailer-Jones


Stars which pass close to the Sun could have a noticeable impact on the solar system. For example, if close, slow, and massive enough, they could perturb the paths of Oort cloud objects, sending them into the inner solar system where they become visible as long-period comets. The precise astrometry from Gaia makes it possible to perform a large-scale systematic search for such stars, and on a much larger scale than was done with Hipparcos.

A new study has done just this with data from the first Gaia data release, by combining the five-dimensional phase space information in the TGAS catalogue - positions, parallaxes, proper motions - with radial velocities from other surveys. The motions relative to the Sun of over 300 000 TGAS stars were traced through the Galaxy and their closest approach to the Sun - in the past or future - determined. 97 stars (corresponding to the open circles in the figure above) were found which will pass within 5pc of the Sun (5pc translates to about 154 trillion kilometres or 154 x 1012 kilometres). Among these is the well-studied future encounter Gliese 710, now found by Gaia to come much closer than previously known, at a distance of just 0.05pc to 0.076pc or about 1.5 to 2.25 trillion kilometres.

But beyond just finding encounters among what TGAS could observe, this study corrected for what TGAS could not observe in order to infer the overall rate of close stellar encounters. This was done by adopting a simple model of the positions and motions of stars, and then seeing how the distribution of their perihelion parameters is changed by the TGAS selection function. This incompleteness is shown as the background colour scale in the figure (and is primarily due to the fact that TGAS does not include stars outside the approximate range G=4.5 to G=13.5).

By combining this incompleteness map with the observed distribution of encounters (and considering also that only 16% of TGAS stars have radial velocity measurements), the overall current rate of encounters could be inferred. This was found to be 545 ± 59 stars per million year coming with 5pc. The number is expected to scale quadratically with distance, so would correspond to (for example) 21.8 ± 2.4 stars per million year with 1pc. This includes all types of stars, and is somewhat higher than previous estimates.

This study will receive a huge boost with the second Gaia data release. That release will not only contain full astrometry on many more (and more distant) stars; it will also include radial velocities on several million stars. The selection function should also be better defined, meaning that a more reliable estimate of the encounter rate can be derived.

Two press releases came along with this story, one by MPIA and one on the ESA portal. For more in-depth information, please have a look at the article "The completeness-corrected rate of stellar encounters with the Sun from the first Gaia data release" or get in contact with C.A.L. Bailer-Jones.

Credits: ESA/Gaia/DPAC, Coryn Bailer-Jones, Max Planck Institute for Astronomy, Heidelberg, Germany

[Published: 31/08/2017]


Image of the Week Archive

31/08: Close stellar encounters from the first Gaia data release
16/08: Preliminary view of the Gaia sky in colour
07/07: Chariklo stellar occultation follow-up
24/04: Gaia reveals the composition of asteroids
20/04: Extra-galactic observations with Gaia
10/04: How faint are the faintest Gaia stars?
24/03: Pulsating stars to study Galactic structures
09/02: Known exoplanetary transits in Gaia data
31/01: Successful second DPAC Consortium Meeting
23/12: Interactive and statistical visualisation of Gaia DR1 with vaex
16/12: Standard uncertainties for the photometric data (in GDR1)
25/11: Signature of the rotation of the galactic bar uncovered
15/11: Successful first DR1 Workshop
27/10: Microlensing Follow-Up
21/10: Asteroid Occultation
16/09: First DR1 results
14/09: Pluto Stellar Occultation
15/06: Happy Birthday, DPAC!
10/06: 1000th run of the Initial Data Treatment system
04/05: Complementing Gaia observations of the densest sky regions
22/04: A window to Gaia - the focal plane
05/04: Hipparcos interactive data access tool
24/03: Gaia spots a sunspot
29/02: Gaia sees exploding stars next door
11/02: A new heart for the Gaia Object Generator
04/02: Searching for solar siblings with Gaia
28/01: Globular cluster colour-magnitude diagrams
21/01: Gaia resolving power estimated with Pluto and Charon
12/01: 100th First-Look Weekly Report
06/01: Gaia intersects a Perseid meteoroid
18/12: Tales of two clusters retold by Gaia
11/11: Lunar transit temperature plots
06/11: Gaia's sensors scan a lunar transit
03/11: Celebrity comet spotted among Gaia's stars
09/10: The SB2 stars as seen by Gaia's RVS
02/10: The colour of Gaia's eyes
24/09: Estimating distances from parallaxes
18/09: Gaia orbit reconstruction
31/07: Asteroids all around
17/07: Gaia satellite and amateur astronomers spot one in a billion star
03/07: Counting stars with Gaia
01/07: Avionics Model test bench arrives at ESOC
28/05: Short period/faint magnitude Cepheids in the Large Magellanic Cloud
19/05: Visualising Gaia Photometric Science Alerts
09/04: Gaia honours Einstein by observing his cross
02/04: 1 April - First Look Scientists play practical joke
05/03: RR Lyrae stars in the Large Magellanic Cloud as seen by Gaia
26/02: First Gaia BP/RP deblended spectra
19/02: 13 months of GBOT Gaia observations
12/02: Added Value Interface Portal for Gaia
04/02: Gaia's potential for the discovery of circumbinary planets
26/01: DIBs in three hot stars as seen by Gaia's RVS
15/01: The Tycho-Gaia Astrometric Solution
06/01: Close encounters of the stellar kind
12/12: Gaia detects microlensing event
05/12: Cat's Eye Nebula as seen by Gaia
01/12: BFOSC observation of Gaia at L2
24/11: Gaia spectra of six stars
13/11: Omega Centauri as seen by Gaia
02/10: RVS Data Processing
12/09: Gaia discovers first supernova
04/08: Gaia flag arrives at ESAC
29/07: Gaia handover
15/07: Eclipsing binaries
03/07: Asteroids at the "photo finish"
19/06: Calibration image III - Messier 51
05/06: First Gaia BP/RP and RVS spectra
02/06: Sky coverage of Gaia during commissioning
03/04: Gaia source detection
21/02: Sky-background false detections in the sky mapper
14/02: Gaia calibration images II
06/02: Gaia calibration image I
28/01: Gaia telescope light path
17/01: First star shines for Gaia
14/01: Radiation Campaign #4
06/01: Asteroid detection by Gaia
17/12: Gaia in the gantry
12/12: The sky in G magnitude
05/12: Pre-launch release of spectrophotometric standard stars
28/11: From one to one billion pixels
21/11: The Hipparcos all-sky map
15/10: Gaia Sunshield Deployment Test
08/10: Initial Gaia Source List
17/09: CU1 Operations Workshop
11/09: Apsis
26/08: Gaia arrival in French Guiana
20/08: Gaia cartoons
11/07: Model Soyuz Fregat video
01/07: Acoustic Testing
21/06: SOVT
03/06: CU4 meeting #15
04/04: DPCC (CNES) 
26/03: Gaia artist impression 
11/02: Gaia payload testing  
04/01: Space flyby with Gaia-like data
10/12: DPAC OR#2. Testing with Planck
05/11: Galaxy detection with Gaia
09/10: Plot of part of the GUMS-10 catalogue
23/07: "Gaia" meets at Gaia
29/06: The Sky as seen by Gaia
31/05: Panorama of BAM clean room
29/03: GREAT school results
12/03: Scanning-law movie
21/02: Astrometric microlensing and Gaia
03/02: BAM with PMTS
12/01: FPA with all the CCDs and WFSs
14/12: Deployable sunshield
10/11: Earth Trojan search
21/10: First Soyuz liftoff from the French Guiana
20/09: Fast 2D image reconstruction algorithm
05/09: RVS OMA
10/08: 3D distribution of the Gaia catalogue
13/07: Dynamical Attitude Model
22/06: Gaia's view of open clusters
27/05: Accuracy of the stellar transverse velocity
13/05: Vibration test of BAM mirrors
18/04: L. Lindegren, Dr. Honoris Causa of the Observatory of Paris
19/01: Detectability of stars close to Jupiter
05/01: Delivery of the WFS flight models
21/12: The 100th member of CU3
17/11: Nano-JASMINE and AGIS
27/10: Eclipsing binary light curves fitted with DPAC code
13/10: Gaia broad band photometry
28/09: Measuring stellar parameters and interstellar extinction
14/09: M1 mirror
Please note: Entries from the period 2003-2010 are available in this PDF document.