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I saw this picture of M51 (Whirlpool galaxy) and noticed many, many bright dots around and in the galaxy. I have freehand-circled a few as examples. Are these individual stars (probably supergiants) in the Whirlpool Galaxy, or are they clusters, stars in the Milky Way, or something else?

Potential stars
Source: ESA/Hubble

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    $\begingroup$ You noticed a red object on the lower left of the image, which excludes clusters. I would suspect they are foreground stars. You could check their positions in any astronomical positioning database, or the free Stellarium app. $\endgroup$
    – AtmosphericPrisonEscape
    Commented Mar 23, 2021 at 22:16
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    $\begingroup$ I just opened Stellarium and I could relate most to a foreground star. That doesn't mean the others aren't foreground stars either. It's not completely impossible that they're very bright stars like Cepheids in M51, too. $\endgroup$
    – planetmaker
    Commented Mar 23, 2021 at 23:40
  • $\begingroup$ Some of them have a distinct diffraction cross, so likely foreground stars. Some are more diffused, could they be clusters of Whirlpool? $\endgroup$
    – Alchimista
    Commented Mar 24, 2021 at 12:23

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A query to the Gaia Archive within 6 arc min of target name M51 finds 20 sources with phot_g_mean_mag <= 17. Aladin Lite helps to locate them visually. Five are circled in the lower half of the image in question:

Gaia source_id ra ° dec ° parallax (mas) magg
1551894661845524736 202.4034 47.1522 8.854 ± 0.017 14.3
1551988532650838016 202.4205 47.1790 2.387 ± 0.041 16.4
1551988670089792256 202.4236 47.1979 0.632 ± 0.025 15.1
1551988425277200640 202.4323 47.1537 0.813 ± 0.025 15.2
1551988567010595840 202.4417 47.1800 1.536 ± 0.012 13.3

These parallaxes indicate distances between 113 and 1600 parsecs, well within the Milky Way.

Of the three sources circled in the upper half, two seem to be listed in Gaia EDR3 but do not have good parallaxes there. Aladin Lite shows SIMBAD matches near all three in Hwang and Lee 2008, a catalog of 2200 star clusters in M51.

HL2008 id ra ° dec ° magV Gaia source_id
89770 202.494 47.216 20.0 1551988944968489984
13162 202.505 47.154 21.1 --
28066 202.531 47.167 19.8 1551987909882986368
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