# How far have individual stars been seen by radio telescopes?

Writing this answer got me thinking.

As far as I understand it, stars themselves radiate most of their energy at optical wavelengths (near-IR through near-UV).

Various types of stellar objects may flare in various ways when in-falling matter from an accretion disk or companion is heated in magnetic fields or undergoes transient nucleosynthesis, but I'm excluding these types of processes and asking only about radiation from the stellar object itself, in steady-state.

Question: How far have individual stars been seen by radio telescopes?

• – Keith McClary Jul 13 '19 at 1:03
• @KeithMcClary hmm... "virtually only" hmm... – uhoh Jul 13 '19 at 1:06
• Also, "regular" and "steady-state". Wiki's source says "few 'adult' stars emit enough radio energy to be detected". – Keith McClary Jul 13 '19 at 1:17
• P.3 here seems to say that the masing occurs thousands of AU from the star. Is that "from the stellar object itself" ? – Keith McClary Jul 26 '19 at 0:07
• Another approach is to look at which Emission Mechanisms can happen on "the stellar object itself". – Keith McClary Jul 26 '19 at 18:13

Some types of red giant stars are susceptible to intense water and silicon oxide MASER activity in their outer envelopes. This results in intense radio emission. Examples of such maser activity have been observed in the Small Magellanic Cloud,at a distance of $$\sim 60$$ kpc (e.g. van Loon 2013).

Click for full size.

IRAS 05298−6957 (van Loon 2013): Note the logarithmic wavelength axis; the water maser peak lies at about 18 cm / 1670 MHz.

• Thanks, this is just what I was looking for. – uhoh Jul 25 '19 at 21:01
• Wow. I guess this means we have no actual proof that other Galaxies are made of stars! – SurpriseDog Jul 26 '19 at 12:06
• @Benjamin Other stars can be observed in other galaxies, just not at radio wavelengths. – ProfRob Jul 28 '19 at 14:56
• @RobJeffries I was under the impression that Radio Telescopes had the highest resolution due to interferometry working for them. That's why the telescope that imaged the black hole in another galaxy (the EHT) was as radio interferometry telescope. – SurpriseDog Jul 28 '19 at 15:01
• Stars are much less luminous at radio wavelengths. Cepheid variables were identified in other galaxies in 1908. en.wikipedia.org/wiki/Henrietta_Swan_Leavitt – ProfRob Jul 29 '19 at 9:13

From Vega stars types, observations studies, include star HD 23362 (Table I.) with a distance 1004 light years