Legacy Discoveries

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The timeline below shows a brief description of the most important discoveries of the Arecibo Observatory.

"Please enjoy reading about the remarkable science done at the Arecibo Observatory. I hope the discoveries inspire you as much as they inspire me."

- Dr. Joan T. Schmelz


  • 2017

    Arecibo discovered two extremely strange pulsars that undergo a “cosmic vanishing act;” sometimes they are there, and then for very long periods of time, they are not.

    -This has upended the widely held view that all pulsars are the orderly ticking clocks of the universe.

  • 2016

    Arecibo weighed in on the controversy surrounding the possible variability of the fine structure constant, a, which describes the electromagnetic interaction between elementary charged particles.

    -150 hours of observing time at Arecibo revealed that a has not changed by more than 1.3 parts in a million in these three billion years.

  • 2016

    Arecibo-RadioAstron VLBI observations of quasar 3C273 revealed a brightness temperature greater than 1013 K.

    -This temperature is so high that it forces astronomers to question the traditional model - synchrotron radiation - for the emission emanating from the vicinity of the supermassive black hole.

  • 2016

    Arecibo discovered the first ever repeating Fast Radio Burst.

    - FRBs are millisec-duration, radio pulses that appear to be extragalactic.
    - The repeater demonstrates that its source survives the bursts and rules out a class of models requiring
    catastrophic explosions.

  • 2015

    NANOGrav (North American Nanohertz Obs for Gravitational Waves) uses an array of high-precision millisec pulsars to search for gravitational waves from supermassive black hole binaries.

    - Upper limits are already constraining models of space-time strain.

  • 2014

    Arecibo was essential for VLBI result that resolved the Pleiades distance controversy with measurements of ultra-faint radio stars.

    - This distance was just confirmed by the Gaia Collaboration.

  • 2014

    The GALFA (Galactic Arecibo L-Band Feed Array) survey revealed slender HI structures in interstellar space that are well aligned with dust polarization & the magnetic field.

    - We can now measure the foreground dust signal more precisely, improving our ability to uncover the B-mode signature of inflation.

  • 2013

    Arecibo begins timing a pulsar in a triple system.

    - This will provide the best test for the strong equivalence principle, an order on magnitude better than the Sun-Earth-Moon system.

  • 1992

    Arecibo discovered the first ever exoplanet.

    In subsequent observations, an entire planetary system was found around the pulsar PSR 1257+12.

  • 1992

    Arecibo discovered ice at the North and South poles of Mercury.

    - The ice persists in shadowed craters despite the high temperatures, 800°F, at the surface; this discovery was confirmed in 2014 by NASA’s MESSENGER spacecraft.

  • 1982

    Arecibo discovered the first OH Megamaser in Arp 220, the nearest ultraluminous IR galaxy.

    - Arp 220 is a merger undergoing a burst of star formation; the population inversion is produced by IR radiation from dust.

  • 1982

    Arecibo discovered the first millisecond pulsar, PSR 1937+21.

    - This discovery of a second class of pulsar led to the suggestion that pulsars can spin-up by accreting mass from a companion.

  • 1981

    Arecibo produced the first radar maps of the surface of Venus.

    - Optical images show only the top of the thick cloud layer.

  • 1974

    September 2007 - May 2010

    Arecibo discovered the first ever binary pulsar. Changes in periastron confirmed the predictions of General Relativity.

    - The 1993 Nobel Prize in Physics was awarded to Hulse and Taylor for this discovery.

  • 1968

    Arecibo measured the 33-ms period of the Crab pulsar.

    - Only sporadic radio pulses from the Crab nebula supernova remnant were know before Arecibo.

  • 1967

    September 2007 - May 2010

    Arecibo discovered that the rotation rate of Mercury is 59 days, not the previously estimated value of 88 days.

    - The rotation is not tidally locked, but rather, the rate is an orbital resonance with 2 orbits for every 3 rotations.