The Quiet Galaxy

The equation · piece 1 of 7 · R*

How many stars are born in the galaxy each year

The rate at which the Milky Way makes new stars, averaged over the time it takes a star to grow a civilisation. It is the best-measured factor in the equation: the galaxy's output of new stars is read from the glow of young stars and the gas they heat, and comes to roughly one and a half to two solar masses a year, which is three or four stars a year once the many small stars are counted. The one real argument is over which rate to use: today's, or the higher average over the galaxy's whole life, since the stars that could host a civilisation today were mostly born billions of years ago.

The range this site uses 1 to 20 stars a year reviewed
set on 17 October 2026

When the number on the home page is computed, a value for this piece is picked at random from this range each time, and every tenfold step between the two ends is equally likely.

Why that range

Narrower than the 2018 paper's 1 to 100: the top of their span is far above any measurement of this galaxy. Measurements of today's rate (Robitaille and Whitney 2010, Licquia and Newman 2015, Quintana and others 2025) cluster between 1.3 and 3.7 stars a year. The range reaches up to 20 for two reasons. The stars that could host a civilisation today were mostly born long ago, when the galaxy made stars faster: spreading its roughly six times ten to the tenth solar masses of stars over its ten billion years gives an average of about six solar masses, or ten stars, a year. And the 2023 measurement of the galaxy's aluminium-26 glow (Siegert and others) gives 8 to 16 stars a year, which a range meant to cover the published argument has to hold; it is one method, and its authors flag a possible foreground that could make the true figure lower, so 20, a round step, is used rather than 16. Drake's 1961 value of one star a year is the floor, and the 2025 census (1.3) sits just above it. Evenly spread across powers of ten, the same shape the 2018 paper used, because the question is which power of ten, not which digit. The top was 10 until 2026-10-17, when it rose to 20 (ruled by John 2026-10-17 on the outside review, items 2 and 4).

Rests on: Sandberg and others, 2018; Siegert and others, 2023.

The published estimates

6 estimates on the record, oldest first. Each says who made it, when, how, and where to find it. A range is set from these by hand, with the reason above, never computed from them: the reason is the arguable part.

WhenWhoEstimateHow it was reached
1961 Frank Drake and the Green Bank meetingGreen Bank meeting of November 1961, as recorded in Drake and Sobel, Is Anyone Out There? (Delacorte, 1992), pages 55 to 62; the meeting's record is the founding entry of the publications log (drake-1961) 1 stars a year One star a year on average over the life of the galaxy, which the meeting regarded as conservative.
February 2010 Thomas Robitaille and Barbara WhitneyRobitaille and Whitney, 'The present-day star formation rate of the Milky Way determined from Spitzer-detected young stellar objects', Astrophysical Journal Letters 710, L11 (2010) 1.4 to 2.9 stars a year Counted the young stars the Spitzer space telescope sees across the galactic plane and compared the count with a model of how such stars form and fade; 0.68 to 1.45 solar masses of new stars a year, which is 1.4 to 2.9 stars a year at the usual average of half a solar mass per new star.
June 2015 Timothy Licquia and Jeffrey NewmanLicquia and Newman, 'Improved estimates of the Milky Way's stellar mass and star formation rate from hierarchical Bayesian meta-analysis', Astrophysical Journal 806, 96 (2015) 2.9 to 3.7 stars a year Combined every earlier measurement of the galaxy's star-formation rate, allowing for the chance that any one of them is wrong; 1.65 plus or minus 0.19 solar masses a year, which is 2.9 to 3.7 stars a year at half a solar mass per star.
June 2018 Anders Sandberg, Eric Drexler and Toby OrdSandberg, Drexler and Ord, 'Dissolving the Fermi Paradox', arXiv:1806.02404 (2018), Table 1 (sandberg-2018) 1 to 100 stars a year A deliberately wide span, evenly spread across its powers of ten, meant to cover the whole published argument rather than to measure anything; the paper itself notes that the real uncertainty is about one power of ten.
January 2023 Thomas Siegert and othersSiegert and others, 'Galactic 26Al traces metal loss through hot chimneys', Astronomy and Astrophysics 672, A54 (2023) (siegert-2023) · in the log 8 to 16 stars a year Measured the gamma-ray glow of radioactive aluminium made by massive stars across the galaxy and worked back to how fast stars must be forming to keep it topped up; 4 to 8 solar masses of new stars a year, which is 8 to 16 stars a year at half a solar mass per star. One method, and above the several that agree on 1 to 4; added at John's ruling on 2026-10-16 after the first weekly reading found it.
March 2025 Alexis Quintana and othersQuintana and others, 'A census of OB stars within 1 kpc and the star formation and core collapse supernova rates of the Milky Way', Monthly Notices of the Royal Astronomical Society (2025) (quintana-2025) · in the log 1.3 stars a year Counted the massive, short-lived stars within about three thousand light years of the Sun and scaled the count to the whole galaxy; 0.67 solar masses a year, which is 1.3 stars a year at half a solar mass per star. Added at John's ruling on 2026-10-16 after the first weekly reading found it.

What would move this

The discovery that would narrow the range

A new measurement of the Milky Way's present star-formation rate, or of its star-formation history, that falls outside one to twenty stars a year.

When a paper or a survey of that kind is published, it is logged in the story so far with a note saying whether it moved this range. A move is written as a dated revision below, with the old number, the new one and the reason.

The last reading

Once a week the records are read against the news, each against the test above. Open a line to see what that week held. Every reading ever made of this record is on the reading page.

  • 2026-10-16 Ruled By hand

    No new measurement of the galaxy's star-formation rate appeared in the window. Two measurements the record does not carry were found: Siegert and others (2023, from the gamma-ray glow of radioactive aluminium) give 4 to 8 solar masses a year, about 10 to 20 stars a year, above the range's top of 10; Quintana and others (2025, from a census of massive stars within a kiloparsec) give 0.67 solar masses a year, inside the range on its low side. Both are logged.

    For me: The reading would have raised the range's top from 10 to 20 stars a year on the 2023 aluminium-26 result, which is inside the cap of one tenfold step, but did not: the paper is from 2023, not this window, it is one method against several that agree on 1 to 4 stars a year, and the session that ran this reading was told not to edit the factor records while other sessions hold them. Your call whether the top rises to 20 (the 2018 paper's own range runs to 100), and whether the two measurements go into the record's estimate list.

    Taken off my list on 2026-10-16, by a ruling recorded on the record.

    Siegert, 2023Quintana, 2025 source 1source 2

How the range has moved

DateWhatFromToWhy
16 October 2026 estimate four published estimates six published estimates: the 2023 aluminium-26 measurement (8 to 16 stars a year) and the 2025 massive-star census (1.3 a year) added The weekly reading of 2026-10-16 found two measurements the record did not carry and flagged the range for John. He ruled on 2026-10-16: add both to the estimate list and leave the range's top at 10 until the outside review of the seven ranges.Because of Galactic Population Synthesis of Radioactive Nucleosynthesis Ejecta.
17 October 2026 range.high 10 20 Ruled by John 2026-10-17 on the outside review (items 2 and 4 of docs/reviews/2026-10-17-rulings.md): the 2023 aluminium-26 measurement gives 8 to 16 stars a year, above the old top of 10, and the weekly reading of 2026-10-16 had flagged the same. The floor of 1 holds (the 2025 census gives 1.3) and the shape stays log-uniform.Because of Galactic Population Synthesis of Radioactive Nucleosynthesis Ejecta.
17 October 2026 what_would_move_this falls outside one to ten stars a year falls outside one to twenty stars a year Ruled by John 2026-10-17 on the outside review (item 4): the test line names the range's ends, so it follows the top.
17 October 2026 range.status first-pass reviewed The outside review of the seven ranges ran on 2026-10-17 and John ruled on every item the same day (docs/reviews/2026-10-17-rulings.md).

The explanations that lean on this piece

No explanation on the record bears on this piece yet.

The papers that bear on it

Notes

Carl Sagan's version of the equation in Cosmos (1980) replaces this factor with the total number of stars in the galaxy and asks what fraction of a planet's life a civilisation lasts, so his numbers do not translate to a rate per year and are not listed here. Westby and Conselice (2020) likewise work from the galaxy's star-formation history rather than a single rate. Checked 2026-10-16: Robitaille and Whitney's 0.68 to 1.45, Licquia and Newman's 1.65 plus or minus 0.19 and their stellar mass of 6.08 plus or minus 1.14 times ten to the tenth solar masses, and Kennicutt and Evans's mean star mass of 0.5 solar masses are all in the papers' own text. Open and not changed here: Drake's 1961 value is recorded as 1 star a year, but the Cambridge abstract of the star-formation chapter of the 2015 Drake volume says 'ten stars per year' and Glade and colleagues (2012, Table 1) give 10; the book could not be opened tonight, so the estimate and the range (whose reasoning does not depend on it) should be revisited once it is. Written 2026-10-16. Outside review, 2026-10-17: the top of the range rose from 10 to 20 (items 2 and 4); the reviewer's proposal to change the shape to uniform (item 1) was declined because a uniform span from 1 to 20 puts more than half its weight above 10, where one method sits and five do not, whereas the question is still which power of ten (headline with a uniform shape on a scratch copy: 56% alone in the galaxy); ruled by John 2026-10-17.

Claims still to be checked

These were written from memory and have not yet been checked against a source. A later pass clears each one.

  • Ruiz-Lara and colleagues (2020, ruiz-lara-2020) is logged for this factor, but whether its full text gives a rate for the whole galaxy in stars a year (it reconstructs the star-formation history of a region of about 2,000 parsecs around the Sun, with bursts about 5.7, 1.9 and 1.0 billion years ago) has not been read; the reviewer's remark that the bursts ran at 'about four times the normal rate' was not found in the abstract or in coverage. Until the full text is read there is no estimate to add. Raised 2026-10-17 by the outside review (item 3); open.

Think the range should move? Argue it, with a source. Spotted an error on this page? Say so. Or read how disagreement gets folded in. The record itself is data/factors/star-formation.toml in the public repository.