Selena Gomez in the Studio as Ariana Dethrones Her on Instagram

Selena Gomez is back in the studio, and the timing couldn't be more perfect -- 'cause, as of this week, Ariana Grande's more relevant ... on Instagram, anyway.

Selena was seen leaving a recording studio in L.A. Tuesday night, and ya gotta imagine she hopped into the booth and laid down some tracks. It's been more than 3 years since she released a solo album, even if she's been featured here and there with folks like Cardi B.

Funny enough ... as Selena was in that studio, AG surpassed her fellow pop star in IG followers to become the most followed woman, if only barely. On Tuesday, Ariana reportedly hit 146,286,173 compared to Selena's 146,267,801. Both ladies got nothin' on Cristiano Ronaldo, though ... who's sitting pretty at 156M-plus followers.

Speaking of Ariana, she was seen leaving a rehearsal Tuesday in Calabasas as she prepares to head out on tour. Followers or not ... the hustle never seems to stop in this biz.

Not to compare these talented ladies, but they've simply had a much different past couple years ... although neither has escaped hardship.

Selena received mental health treatment last year after having an emotional breakdown. She also had a major surgery in 2017 for a kidney transplant. As for Ari, she lost her ex-BF, Mac Miller, to an accidental overdose, and split with her fiance, Pete Davidson.

Here's hoping Selena's got new tunes on the horizon. It'd be great to hear her over the airwaves again.