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We are Not Alone: Our Sun Escaped From Galactic Central Region Together with Stellar “Twins”

Date
March 13, 2026
Researchers
Daisuke Taniguchi (Tokyo Metropolitan University, Assistant Professor)
Takuji Tsujimoto (NAOJ, JASMINE Project, Assistant Professor)

Abstract

Analysis of Gaia satellite’s big data allowed us to build the world’s largest, high-confidence catalog of solar twin stars, offering new insights into the mechanisms behind the Solar System’s migration. The results suggest that the Solar System may have undergone rapid Galactic migration shortly after its formation, traveling over 10,000 light years within the Milky Way. This provides clues to how the Solar System became a planetary system capable of supporting life. Future investigations with JASMINE are expected to provide even deeper insights.

Artist's impression of a mass migration

Fig.1 : A mass migration of stellar twins. Stars similar to our Sun form a mass migration from the central region of the Milky Way Galaxy, occurring approximately 4 to 6 billion years ago (Credit: NAOJ). See the concept video below.

Contents

The fundamental questions —“Where did we come from? Who are we? Where are we going?”— are addressed in this study from the perspective of the Solar System’s origin. The Solar System is believed to have formed about 4.6 billion years ago near the Galactic center and later migrated over 10,000 light years to its current location. However, the timing and mechanism of this “great migration” have long remained unclear.

A research group led by Assistant Professors Daisuke Taniguchi (Tokyo Metropolitan University) and Takuji Tsujimoto (NAOJ) constructed a high-confidence catalog of 6,594 solar twins1, i.e., stars with properties extremely similar to the Sun, using the large-scale GSP-Spec2 dataset from the Gaia satellite3. This catalog contains about 30 times more stars than the largest previous datasets. After statistically correcting for observational biases, the team discovered that many solar twins born approximately 4-6 billion years ago, including the Sun’s age, are present near the Solar System.

The presence of many stars of the same age provides important clues to the Solar System’s migration history. The team proposes that the formation of the Milky Way’s central bar4 triggered large-scale migration of the Solar System and numerous solar twins soon after their birth (Fig. 2). This rapid migration could have moved the Solar System away from the energetically hostile central regions to the safer outer disk, allowing the Earth to maintain stable conditions for billions of years – potentially critical for life.

Mass stellar migration model

Fig.2 : The mass stellar migration model proposed by this research. BYA = billion years ago. (Credit: NAOJ)

Background

The Solar System currently orbits within the Galactic disk at a distance of about 27,000 light years from the center of the Milky Way. However, comparisons of the Sun’s age and metallicity with those of other stars suggest that the

Solar System was actually born closer to the Galactic center, at a distance of less than about 20,000 light-years. In other words, during its lifetime of 4.6 billion years, the orbital radius of the Solar System is thought to have increased by more than 10,000 light years, implying that it has undergone significant radial migration5.

However, it has been pointed out that such a large migration of the Solar System would be extremely difficult. The Galactic bar, which currently rotates in the central region of the Milky Way, is theoretically expected to create a barrier near its outer region, known as the corotation barrier6 (Fig. 3). As a result, the probability that the Solar System, if it formed inside this barrier, could migrate outward to its present location is considered to be very low.

This raises an intriguing question: Was the Solar System’s migration merely a product of chance? Or were we guided here by some underlying mechanism?

Solar System and its birthplace

Fig.3： Current Solar System location (blue) and estimated birth location (red). The corotation barrier of the Galactic bar (yellow) can impede migration from the birth location to the present position (Credit: NASA/JPL-Caltech/ESO/R. Hurt, modified by authors).

Details of the Study

The research team focused on a special class of stars known as solar twins, stars that closely resemble the Sun. Because their colors and luminosities are nearly identical to those of the Sun (Fig. 4, left), solar twins allow astronomers to investigate both individual stellar properties and their statistical characteristics with exceptionally high precision. However, previous studies were limited by small sample sizes and uncertain stellar ages, making comprehensive statistical analyses difficult.

Solar Twins

Fig.4 : Solar Twins (Left) The relationship between color and luminosity for various types of stars. Solar twins refer to stars with colors and luminosities similar to the Sun (stars within the red trapezoid). (Right) Distance histogram of solar twins obtained in this study (blue). Compared with previous spectroscopic studies of individual stars (black), we have successfully constructed a sample approximately 30 times larger.

To overcome these limitations, the research team turned to the Gaia astrometry satellite, launched by the European Space Agency (ESA). In particular, they focused on the spectroscopic analysis catalog (GSP-Spec) included in Gaia’s third data release (DR3) published in June 2022. From the approximately 5.6 million stars contained in the GSP-Spec dataset, the team systematically identified solar twins. As a result, they successfully constructed a catalog of 6,594 solar twins located within about 1,000 light years of the Solar System. This sample is roughly 30 times larger than the largest high-confidence samples used in previous studies (Fig. 4, right). The ages of these solar twins were then determined based on stellar evolution models.

In astronomical observations, unavoidable biases are present in the data. For example, brighter stars are more likely to be detected than fainter ones. To address this issue, the researchers first quantified how easily stars of different ages are observed. They then applied techniques originally developed in signal and image processing to correct for these observational biases. This approach enabled them to reconstruct the true age distribution of solar twins (Fig. 5, top).

The reconstructed distribution revealed two notable features:

  1. a sharp peak at around 2 billion years
  2. a broad bump spanning roughly 4–6 billion years

The former feature has been observed previously in studies of stars other than solar twins and has been discussed in connection with events such as the interaction between the Milky Way and the Sagittarius dwarf galaxy. The research team focused instead on the latter feature: the broad bump that had largely gone unnoticed in earlier studies. Its age range of 4–6 billion years closely matches the age of the Sun (4.6 billion years). This finding indicates that many Sun-like stars of the same generation as the Sun exist in the immediate vicinity of the Solar System. In other words, we are not alone.

Age distribution of Solar Twins

Fig.5 :（Top）The intrinsic age distribution of solar twins, obtained by correcting observational biases using two different methods. (Bottom) The broadening of the age distribution is thought to result from the formation of the Galactic bar, which triggered the birth of the Sun and numerous solar twins and caused them to migrate rapidly to the current position of the Solar System. Solar twins are believed to exhibit an inverse correlation between age and birth radius, which is indicated on the upper axis as a reference.

Why is it important that many solar twins of the same generation as the Sun exist in the Solar neighborhood? The reason is that this fact places strong constraints on the Solar System’s “great migration.” Because these solar twins have ages and metallicities very similar to those of the Sun, they are thought to have been born, like the Sun, near the center of the Milky Way and subsequently migrated to their present locations over the course of their lifetimes. This suggests the existence of a universal mechanism that enabled many solar twins to undergo large-scale migration without being blocked by the barrier. In other words, the Solar System was likely not an exceptional case that happened to travel a long distance by chance, but rather one member of a much larger group of stars that migrated together across the Galaxy.

The research team focused on the formation epoch of the Galactic bar as a possible trigger for this large-scale migration. Once the bar becomes dynamically stable, the barrier it creates makes large radial migration difficult. However, previous studies have suggested that during the bar’s formation phase, its dynamical influence may both enhance star formation near the bar and allow stars to migrate radially more efficiently. Then, if the Galactic bar formed about 6–7 billion years ago, the Solar System and many solar twins could have been born near the Galactic center around 4–6 billion years ago, and soon afterward migrated rapidly to their present locations (Figure 1; Figure 5, bottom).

The formation epoch of the Galactic bar has long been debated, with many studies suggesting an age older than about 8 billion years. However, the scenario proposed in this study suggests that the bar may instead have formed about 6–7 billion years ago, offering a new perspective on the current understanding of the Milky Way’s evolution.

Significance and Broader Impacts

By constructing the largest catalog of solar twins ever assembled and applying statistical corrections to observational biases, this study provides new clues to the long journey of the Solar System across the Milky Way. Future high-precision observations of the solar twins identified in this work, particularly those with ages similar to that of the Sun, may reveal true stellar “siblings” that were born in the same region of the Galaxy and at the same time as the Solar System. Identifying such stars could allow astronomers to trace back the birthplace of the Solar System and reconstruct the route of its migration through the Galaxy.

The inner regions of the Milky Way are thought to be a hostile environment for life, where energetic events such as supernova explosions occur far more frequently than in the outer disk. If, as suggested in this study, the Solar System migrated to the Galaxy’s safer outer regions soon after its birth, then its present location may not simply be the result of chance. Instead, the formation of the Galactic bar may have played a crucial role in enabling the Solar System to evolve into a planetary system capable of supporting life. The study also reveals that the Solar System was likely not alone in this journey. Many solar twins appear to have migrated outward together with it. Some of these stars may host planetary systems similar to our own, raising the exciting possibility that Earth-like worlds capable of supporting life could exist among them.

Finally, the results suggest that the Galactic bar may be younger than previously believed. The upcoming JASMINE mission, which will carry out high-precision astrometric observations of the Galactic center, is expected to shed new light on the formation history of the Galactic bar and provide deeper insight into the migration history of the Solar System.

Concept Video

References

  • Paper 1:
    • Title: Solar twins in Gaia DR3 GSP-Spec I. Building a large catalog of solar twins with ages
    • Authors: Daisuke Taniguchi, Patrick de Laverny, Alejandra Recio-Blanco, Takuji Tsujimoto, Pedro A. Palicio
    • Journal: Astronomy & Astrophysics
    • Date: March 12, 2026
    • DOI：10.1051/0004-6361/202658913
  • Paper 2:
    • Title: Solar twins in Gaia DR3 GSP-Spec II. Age distribution and its implication for the Sun's migration
    • Authors: Takuji Tsujimoto, Daisuke Taniguchi, Alejandra Recio-Blanco, Pedro A. Palicio, Patrick de Laverny
    • Journal: Astronomy & Astrophysics (Letter to the Editor)
    • Date: March 12, 2026
    • DOI：10.1051/0004-6361/202658914

Funding

Supported by JSPS KAKENHI (22K18280, 23H00132, 23KJ2149) and the Tokyo Metropolitan University “Chino Miyako Project.”

  1. Solar twins: Solar twins are stars whose atmospheric parameters — effective temperature, surface gravity, and metallicity — are extremely similar to those of the Sun. Other observable properties, such as color and luminosity, are also very close to those of the Sun. By comparing the spectra of solar twins with that of the Sun, astronomers can determine their atmospheric parameters and ages relative to the Sun with exceptionally high precision and reliability. In this study, solar twins are defined as stars whose parameters differ from the Sun by less than 200 K in effective temperature, 0.1 dex in surface gravity, and 0.1 dex in metallicity. ↩

  2. GSP-Spec（General Stellar Parametrizer from Spectroscopy）: GSP-Spec is a catalog that determines stellar atmospheric parameters, chemical abundances, and radial velocities from spectra obtained by the spectrograph onboard the Gaia satellite. In this study, the atmospheric parameters provided in the GSP-Spec catalog were used to estimate the ages of the solar twins. ↩

  3. Gaia satellite: The Gaia satellite, launched by the European Space Agency (ESA) in December 2013, is a space-based astrometry mission designed to map the positions and motions of stars across the entire sky with unprecedented accuracy. By measuring tiny changes in the apparent positions of stars over time, Gaia determines their distances and motions within the Milky Way. The mission also provides spectroscopic observations for millions of stars. This study makes use of Gaia Data Release 3 (DR3), published in June 2022. ↩

  4. Galactic bar: An elongated (elliptical) distribution of stars located at the center of the Milky Way, about 30,000 light-years in length, whose strong gravitational potential influences the motion of stars. ↩

  5. Radial migration: Stars in the Milky Way disk typically follow nearly circular orbits, but their orbital radii can evolve over time. Such variations arise from the gravitational effects of non-axisymmetric structures, including the Galactic bar and spiral arms, as well as from close encounters with massive bodies, such as giant molecular clouds. ↩

  6. Corotation barrier: At the radius where the rotation speed of the bar pattern matches the orbital speed of individual stars (the corotation radius), stars are effectively stationary relative to the bar. As a result, they experience a nearly constant gravitational force from the bar. This tends to trap stars near this radius, creating a barrier that inhibits their radial migration inward or outward. ↩