New View of Young, High-Mass Binary Star at Heart of Orion


A new glimpse inside the heart of Orion has confirmed the separation between the binary star system that orbit each other so closely, astronomers once believed they could be a single star.

The research team, led by Stefan Kraus and Gerd Weigelt from the Max-Planck-Institute for Radio Astronomy (MPIfR) in Bonn, Germany, used ESO’s Very Large telescope Interferometer (VLTI) to obtain the sharpest ever image of the young double star Theta 1 Ori C in the Orion Trapezium Cluster.

The binary stars represent the most massive star in the nearest high-mass star-forming region to Earth. 

Theta 1 Ori C is the dominant and most luminous star in the Orion star nursery. Located at a distance of only about 1,300 light years, it provides a unique laboratory to study the formation process of high-mass stars in detail. The intense radiation of Theta 1 Ori C is ionizing the whole Orion nebula. With its strong wind, the star pair also shapes the famous Orion proplyds, young stars still surrounded by their protoplanetary dust disks.

Although Theta 1 Ori C appeared to be a single star, both with conventional telescopes and the Hubble Space Telescope, the team discovered the existence of a close companion.


“VLTI interferometry with the AMBER instrument allowed us, for the first time, to obtain an image of this system with the spectacular angular resolution of only 2 milliarcseconds”, says Stefan Kraus. “This corresponds to the resolving power of a space telescope with a mirror diameter of 130 meters.”

The new image clearly separates the two young, massive stars of this system. The observations have a spatial resolution of about 2 milliarcseconds, corresponding to the apparent size of a car on the surface of the Moon. 

The VLTI image reveals that in March 2008 the angular distance between the two stars was only about 20 milliarcseconds. Additional position measurements of the binary system have been obtained over the last 12 years using the technique of bispectrum speckle interferometry with 3.6- to 6-meter-class telescopes, allowing high-angular resolution observations even at visual wavelengths down to 440 nm.

The collection of measurements shows that the two massive stars are on a very eccentric orbit with a period of 11 years. Using Kepler’s third law, the masses of the two stars were derived to be 38 and 9 solar masses. Furthermore, the measurements allow a trigonometric determination of the distance to Theta 1 Ori C and, thus, to the very center of the Orion star-forming region.

The resulting distance of 1,350 light-years is in excellent agreement with the work of another research group led by Karl Menten, also from MPIfR, who measured trigonometric parallaxes of the nonthermal radio emission of Orion Nebula stars using the Very Long Baseline Array. These results are important for studies of the Orion region as well as the improvement of theoretical models of high-mass star formation.

The researchers say the results highlight new possibilities of high-resolution stellar imaging achievable with infrared interferometry. The technique allows astronomers to combine the light from several telescopes, forming a huge virtual telescope with a resolving power corresponding to that of a single telescope with 200 meters diameter. 

“Our observations demonstrate the fascinating new imaging capabilities of the VLTI,” said Gerd Weigelt. “This infrared interferometry technique will certainly lead to many fundamental new discoveries.”

LEAD IMAGE CAPTION: VLTI/AMBER image of Theta 1 Ori C in the Orion Trapezium Cluster, plus position measurements of the binary system obtained over the last 12 years. Credit: Max Planck Institute/VLTI/AMBER

Sources: Max Planck Institute press release (emailed through Eurekalert), and the original paper.

13 Replies to “New View of Young, High-Mass Binary Star at Heart of Orion”

  1. Congratulations to all the scientists and engineers of the VLTI team. These early proof-of-concept show that VLTI and other interferometry programs around the world can indeed function reliably enabling astronomers to explore objects at a much greater scale than was ever before possible. Who knows what discoveries lie ahead in the field of astronomical interferometry?

  2. “the angular distance between the two stars was only about 20 milliarcseconds”
    how much is the distance between the two in AU, I wonder?

  3. actually, now that I think of it, I should be able to work it out for myself…..

  4. Using the distance to the Orion Nebula as 389 parsecs or 1270 +/- 76 light-years, means that the trig. parallax is 2.571 mas (milliarcsec.)

    If the principal stars in the Trapezium are; (based on the relative position of STF 748A at 6.55V magnitude)

    Star ……. “. mag Spec Class

    STF 748 AB 08.9 7.49 O7 B1V
    STF 748 AC 13.1 5.06 O7
    STF 748 AD 21.5 6.38 B0.5V
    STF 748 AE 04.5 11.1 O7

    Then the projected distances in AU and light years between the components from A (Mabs=-1.4 Mass=4.5 Solar Masses) is;

    B= 3462 AU (0.055 ly.) Mabs =-1.4; 3.6 Solar Masses
    C= 5095 AU (0.081 ly.) Mabs =-2.9; 6.4 Solar Masses
    D= 8362 AU (0.132 ly.) Mabs =-1.6; 4.7 Solar Masses
    E= 1750 AU (0.028 ly.) Mabs =+3.2; 1.5 Solar Masses

    In physical size, therefore for the Trapezium is about 10,000 AU across.
    The largest estimated minimum orbital period of these stars is about 250,000 years. (about 2.5 times that of Alpha Centauri AB to Proxima) This augers well with the fractional movements so far observed with these stars.
    You could compare these values with the older ones described in the dated “Burnham’s Celestial Handbook” Vol.2 “Orion” on Theta Orionis.

    Note: If value were between 1400 to 1600 light years, these projected separations would be slightly larger.

  5. SalBC=Thank you for the data, it is interesting how technology keeps improving, and able to separate stars relatively close together so far away.

  6. I have actually unconditionally gave Salacious B. Crumb my complete permission to use this information as he saw fit. Also “Southern Astronomical Delights” is not a book but in fact is my own website.
    This actual text you talk about here does NOT appear in my “Southern Astronomical Website” at all. I think you will find this is true looking at my article on “The Orion Nebula: at
    (I have added an Open Note at the bottom of this same page verifying this information is true for you.)

    The words in his response are, as far as I know, were actually his own and as such was not plagiarised from me at all.

    Thanks should be extended to Salacious B. Crumb for pointing the open concern within this post.
    I stand quite happy to be able correct the misunderstanding.

  7. Solacious B….FRAUD!!

    Very nice plagerism… you are almost good at it. You should at least give the real person the credit.

    Every bit of what was posted by this fraud was the work of Andrew James in the book “Southern Astronomical Delights”.

    In fact, another person who posted this same information did give A. James credit at:

    Shame…shame. We always knew you didn’t do your own work… just based on how your grammar changed. Now there is DBO proof.

  8. After just watching the “80 Telescopes around thev World” webcast about the VLTI, I feel even more interested in the technology necessary to make these observations in the first place. Like the also-noted Gravitational Wave observatories, VLTI is very sensitive to disruptions in the the locality of the apparatus. While VLTI is now able to show concrete results of its’ labors, GW observatories are still waiting for a confirmable signal, the wait will be hopefully short (notwithstanding the views of PU, EU, PC etc.). Bring on the GWs!

  9. Sorry. The text written here IS my own, and was not at all plagiarised. (At least I’m happy to play with others!)

  10. Hey Mr.Oblivious
    Why the silence and the lack of posturing now, eh?
    I think you may owe me an apology don’t you think?
    You have been caught once again. Again you keep missing the target! Your out of your depth — so it might be better idea to keep those lips a bit more zipped instead of putting your foot in it.
    Appreciate the support astroron, Ron, or whatever your name is.
    Also I suggest you please MYOB.
    Thank you for your sincere co-operation.

  11. Mr.Obvious Says:
    Solacious B FRAUD! FRAUD! FRAUD.
    You Sir, have a problem.

  12. Very very impressive. High res optical imaging is going to be a huge growth area in the coming years. Can’t wait to see what mysteries the technique helps to unearth…

    “Mr.Obvious Says:
    April 4th, 2009 at 1:38 am

    “Solacious B FRAUD! FRAUD! FRAUD.”

    Spectacularly feeble and childish comeback after getting slammed for your false accusations, sunshine.

Comments are closed.